Glossary

QR code glossary

Short, exact definitions of the words used about QR codes: the parts of the pattern, how content is encoded and protected, how dynamic codes redirect and track scans, and the formats phones act on. Each term opens with a one-sentence definition, then explains how it works and why it matters when you make a code.

33 terms · Sourced from ISO/IEC 18004 and other primary references · Updated October 22, 2026

QR code basics

What a QR code is, how it differs from other barcodes, and the static, dynamic and Micro variants.

2D barcode: A 2D barcode is a barcode that stores data across both the width and the height of its pattern, unlike a 1D (linear) barcode such as a UPC, which stores a short number in the widths of its bars; QR codes, Data Matrix, Aztec and PDF417 are all 2D barcodes.
Dynamic QR code: A dynamic QR code is a QR code that encodes a short link to a redirect service instead of the final content, so the destination can be changed after printing and each scan can be counted, for as long as the service keeps the link active.
Micro QR code: A Micro QR code is a smaller variant of the QR code, defined in the same standard (ISO/IEC 18004), that uses a single finder pattern and a 2-module quiet zone to fit up to 35 digits in a symbol of 11 × 11 to 17 × 17 modules.
QR code: A QR code (Quick Response code) is a square two-dimensional barcode, standardized as ISO/IEC 18004, that stores data such as a web address, contact card or WiFi login in a grid of dark and light squares that a phone camera can read in any orientation.
Static QR code: A static QR code is a QR code whose content, such as a web address, WiFi login or contact card, is encoded directly in the printed pattern, so it works without any service in between but cannot be edited or tracked after it is generated.

Anatomy of a QR code

The parts of the printed pattern: modules, the quiet zone and the function patterns scanners use to read it.

Alignment pattern: An alignment pattern is a small 5 × 5 module square, a dark ring around a light ring around a single dark module, placed at regular intervals inside QR codes of version 2 and above so a scanner can correct for tilt, perspective and curved surfaces.
Finder pattern: A finder pattern is one of the three large concentric squares in the top-left, top-right and bottom-left corners of a QR code, which a scanner uses to detect the code, measure its size and angle, and work out which way up it is.
Format information: Format information is a 15-bit field printed twice in every QR code, beside the finder patterns, that tells the scanner which error correction level and which mask pattern the code uses, so it can be read before any of the data.
Module: A module is a single square cell of a QR code, either dark or light, and the basic unit of the symbol: each one is a bit of data or part of a fixed pattern, and the printed width of one module decides how far away the code can be read.
Quiet zone: The quiet zone is the blank margin that must surround a QR code on all four sides so a scanner can tell where the code begins; ISO/IEC 18004 requires it to be at least 4 modules wide for a regular QR code and 2 modules for a Micro QR code.
Timing pattern: A timing pattern is one of two lines of alternating dark and light modules, one horizontal and one vertical, that run between a QR code’s finder patterns and let a scanner count the rows and columns and find the center of each module.

Encoding and capacity

How content becomes modules: versions, error correction, masking, encoding modes and how much fits.

Data capacity: Data capacity is the most content a QR code can hold, which depends on its version, error correction level and encoding mode; the largest code, version 40 at level L, holds 7,089 numeric digits, 4,296 alphanumeric characters, 2,953 bytes or 1,817 kanji characters.
Encoding modes: Encoding modes are the ways a QR code packs characters into bits: numeric mode for digits, alphanumeric mode for a 45-character set of capital letters, digits and a few symbols, byte mode for any data such as UTF-8 text, and kanji mode for Japanese Shift JIS characters.
Error correction level: An error correction level is the setting, L, M, Q or H, that decides how much redundant data a QR code carries; the four levels let a scanner restore roughly 7%, 15%, 25% and 30% of the code’s codewords when they are damaged, dirty or covered.
Mask pattern: A mask pattern is one of eight fixed patterns that a QR encoder combines with the data area, flipping selected modules, so the finished code avoids large solid blocks, long runs and shapes that look like finder patterns, all of which make a code harder to scan.
QR code version: A QR code’s version is its size on a scale from 1 to 40: version 1 is 21 × 21 modules and each version adds 4 modules per side, up to 177 × 177 at version 40, so a version V code is 17 + 4V modules across.
Reed–Solomon error correction: Reed–Solomon error correction is a family of error-correcting codes, published by Irving Reed and Gustave Solomon in 1960, that QR codes use to add calculated check codewords to their data so a scanner can find and repair codewords it misread.

Dynamic codes and tracking

Short links, redirects, scan analytics, campaign tags and routing scans to different destinations.

A/B testing (QR codes): A/B testing with QR codes means splitting the scans of one printed code between two or more destinations, usually at random by set percentages, to measure which page, offer or message turns more scanners into customers.
Redirect: A redirect is an HTTP response with a 3xx status code and a Location header that tells the browser to load a different address; it is how a dynamic QR code’s short link forwards each scan to the code’s current destination.
Scan analytics: Scan analytics are the records a dynamic QR code’s redirect service keeps each time the code is scanned, typically the time, an approximate location from the IP address, the device, operating system, browser and language, summarized into counts and charts.
Short URL: A short URL is a brief web address, such as example.com/r/A7K2Q9, that a server forwards to a longer destination; dynamic QR codes encode one so the printed pattern stays small and the destination can change without reprinting.
Smart routing: Smart routing is a feature of dynamic QR codes that sends each scan of the same printed code to a different destination according to rules, such as the phone’s operating system, its language setting, the time of day or the scanner’s approximate location; routing by location is often called geo-routing.
Unique scans: Unique scans are an estimate of how many different people or devices scanned a QR code, counting repeat scans from the same scanner once, as opposed to total scans, which count every scan.
UTM parameters: UTM parameters are standard tags, such as utm_source, utm_medium and utm_campaign, added to the query string of a link so web analytics tools such as Google Analytics can tell which campaign, source and placement sent each visitor.

Design and printing

Colors, logos and AI artwork, and what each does to a code’s readability.

AI QR code art: AI QR code art is an image made with a generative AI model so that a working QR code is part of the picture, with the code’s dark and light modules formed by elements of the scene instead of plain squares.
Contrast ratio: Contrast, for a QR code, is the difference in brightness between its dark and light modules; scanners need a large difference, with the dark modules darker than the light ones, and designers often check it with the WCAG contrast ratio, which runs from 1:1 (no difference) to 21:1 (black on white).
Logo in a QR code: A logo in a QR code is an image placed over part of the pattern, usually the center, which works because Reed–Solomon error correction can rebuild the modules the logo hides, provided the logo stays within the correction budget and clear of the finder patterns.

Formats and payloads

Standard content formats phones act on: contact cards, WiFi logins, app links and GS1 product links.

Deep link: A deep link is a link that opens a specific screen or item inside a mobile app, such as a product page, rather than the app’s home screen or a website; in a QR code it is usually an ordinary https address that the phone hands to the installed app.
GS1 Digital Link: GS1 Digital Link is a GS1 standard for writing product identifiers, such as a GTIN with an optional batch or serial number, as an ordinary web address, so one QR code can open a page for shoppers and also give the product number to checkout and supply-chain scanners.
vCard QR code: A vCard QR code is a QR code that contains contact details in vCard format, the standard text format for electronic business cards, so that scanning it makes a phone offer to save the name, phone number, email and other fields as a new contact.
WiFi QR code: A WiFi QR code is a QR code that contains a network’s name, password and security type in the WIFI: text format, such as WIFI:T:WPA;S:Cafe Guest;P:espresso-2026;;, so a phone that scans it can offer to join the network without typing the password.

Security

QR code phishing, and codes that can only be used once.

Quishing: Quishing (QR code phishing) is a phishing attack that uses a QR code to send people to a malicious website, typically a fake login or payment page, often by sticking a fraudulent code over a genuine one or by putting a code in an email where link filters cannot inspect it.
Single-use QR code: A single-use QR code is a code that a system accepts only once, such as an event ticket, coupon or one-time link, with the limit enforced by a server that marks the code’s ID as used, not by the printed pattern, which can be copied and scanned any number of times.

Put the terms to work

The guides apply these ideas step by step, from sizing a printed code to tracking a campaign. Static QR codes are free and unlimited on CirculateQR; dynamic codes add editing after printing, scan analytics and routing.

Read the guides Free QR code generators

Written by the CirculateQR team. Spotted something wrong or out of date? Email support@circulateqr.com. QR Code is a registered trademark of DENSO WAVE INCORPORATED.