The name is not a word in itself, but is an acronym for the English term "Completely Automated Public Turing test to tell Computers and Humans Apart" and as the name suggests is a fully automated process, so no one needs to do any verification whether the test was fraudulent or not.
Websites that use CAPTCHA do this through a provider. It provides a kind of API to which the website connects. The provider then runs the actual test and submits the result back to the website. There are several providers offering CAPTCHA services today, including Google.
reCAPTCHA is the name of a CAPTCHA service provided by Google, and is currently available in two versions: reCAPTCHA v2 and reCAPTCHA v3.
The v2 version was officially released in 2014 in two forms: "I'm not a robot" and "Invisible" captcha check.
The new v3 variant, which is still in use today, uses a score-based algorithm in which a user is given a score between 0 and 1 in decimal format. The closer the score is to 0, the more likely a user is to be a bot.
It is a different type of CAPTCHA from the traditional ones, in that there are no texts to complete or images to confirm, these being hidden to the user.
Using a complex algorithm, it analyzes the behavior on the page to determine whether or not it is similar to a human. Its purpose is to streamline CAPTCHA testing so that it is not annoying to users and safer for website administrators.
However, there are situations where the noCAPTCHA algorithm cannot accurately predict the displayed behavior, so in some cases a traditional CAPTCHA test is displayed to the user.