Turing test we typically define as characteristically human. CAPTCHA is a form of reverse Turing test. Before being allowed to perform some action on a website, the user is presented with alphanumerical characters in a distorted graphic image and asked to type them out. This is intended to prevent automated systems from being used to abuse the site. The rationale is that software sufficiently sophisticated to read and reproduce the distorted image accurately does not exist (or is not available to the average user), so any system able to do so is likely to be a human. Software that could reverse CAPTCHA
Turing degree same level of unsolvability; each Turing degree is a collection of Turing equivalent sets, so that two sets are in different Turing degrees exactly when they are not Turing equivalent. Furthermore, the Turing degrees are partially ordered so that if the Turing degree of a set "X" is less than the Turing degree of a set "Y" then any (noncomputable) procedure that correctly decides whether numbers are in "Y" can be effectively converted to a procedure that correctly decides whether numbers are in "X". It is in this sense that the Turing degree of a set corresponds to its level