Difference between a circuit and a normal function I've seen the word circuit used in many crypto contexts (for example, regarding FHE in this pdf). I've always thought of a circuit as another word for a program or function. But is there a difference - i.e., is there something that a standard function can do that a circuit can't?
A circuit is a representation of a (computable) function. There are many other ways to represent a function (mathematical notation, Turing machines, pseudo-code, etc.), but for some purposes it happens that circuits are the most convenient one.