The process of Partial Evaluation is to evaluate a function "in advance", i.e. before the whole input is known, but when at least some parameters, or some property of the parameters are known.
Also called specialization.
The prime example of Partial Evaluation is that of an interpreter. An Interpreter is a function taking two arguments: (1) the program to interpret and (2) the input of the program. Partially evaluate the interpreter with respect to (1)!