Synthetic secret

Definition
Synthetic secrets are

"items of information created specifically for the purpose of authentication; they typically have no relation to characteristics of the individual or to events in the (human) individual's life. Passwords are a type of synthetic secret (when used properly) and the classic example of the "something you know" approach to authentication."

Overview
"The principal problem with using a synthetic secret for authentication is that because it is unrelated to the individual's life in any meaningful way, it is often difficult to remember. . . . This problem arises because synthetic secrets that are easy to remember are also usually easy for others to discover or guess.