C++20 Concepts: The Definitive Guide
C++20 introduces concepts as a way to write powerful self-documenting templates. At their core, concepts are logical binary expressions that can be used to constrain the template parameters of any class or function template. These logical expressions are evaluated at compile time to determine whether the template parameters satisfy the given constraints.
Source: C++20 Concepts: The Definitive Guide, an article by Rajat Jain.