What does captcha mean?
A captcha is a security test used by websites to verify that a visitor is a real person rather than an automated program. Typically presented as a puzzle — reading distorted characters, clicking on images containing traffic lights or crosswalks, or ticking an 'I'm not a robot' box — it exploits tasks that humans perform easily but bots find difficult. The term originated as an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart, coined around the year 2000 by researchers working on automated form protection. In everyday usage, captcha functions as a common noun, so people speak of 'a captcha' or 'a captcha code', though the fully capitalized acronym CAPTCHA remains widespread, especially in technical writing. Encounters with captchas are a routine part of online life: signing up for services, submitting forms, and logging into accounts frequently require passing one. The word carries no emotional weight of its own, though solving a difficult or repeatedly failing captcha is a familiar minor frustration for internet users.
nounA computer program or test designed to distinguish human users from automated bots, typically by requiring the user to complete a task that is easy for humans but difficult for machines, such as deciphering distorted text or identifying images.
- A challenge–response test used on websites to determine whether a user is a human or an automated bot, often involving distorted text, image recognition, or similar tasks that are easy for humans but hard for computers.
"The website required users to solve a captcha before creating an account."
"I had to fill in a captcha before the site would let me post my comment."
"The login page uses a captcha to block automated credential-stuffing attacks."
Standard plural; simply add -s. Often used when referring to multiple tests across different sites or repeated attempts.
"Some sites make you work through several captchas in a row before granting access."
CAPTCHA stands for 'Completely Automated Public Turing test to tell Computers and Humans Apart' — and every time you squint at distorted letters, you're taking a Turing test without realizing it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of captcha
Captcha began as an acronym — CAPTCHA, standing for Completely Automated Public Turing test to tell Computers and Humans Apart — coined around the turn of the millennium by a team including Luis von Ahn and others at Carnegie Mellon University, building on Alan Turing's earlier work on distinguishing machine from human behaviour. The underlying root traces back to the Latin verb capere, meaning 'to take' or 'to seize', which also gives English words such as capture, captive, and captivity. Over time the capitalized acronym has softened into a lowercase common noun in everyday use, while retaining its original all-caps form in technical documentation.
How captcha is actually used
Captcha is a technical/informal noun most commonly encountered in web contexts. It is usually written in all caps as CAPTCHA when referring to the acronym itself; lowercase 'captcha' is common when referring to an instance of the test. It is countable — one can speak of 'a captcha' or 'multiple captchas'. The word has no strong regional variation.
Easily confused with captcha
Capture means to seize, catch, or record something, while captcha is a specific security test used to verify that an online user is human.
Gotcha refers to a catch or unexpected difficulty (or the act of catching someone out), whereas captcha is specifically a human-verification challenge on websites.