The Free On-line Dictionary of Computing (30 December 2018):

inline
unfold

    (Or "unfold") To replace a function call with
   an instance of the function's body.  Actual argument
   expressions are substituted for formal parameters as in
   beta reduction.  Inlining is usually done as a
   compile-time transformation.

   If done recklessly (e.g. attempting to inline a recursive
   function) the compiler will fail to terminate.  If done
   over-enthusiastically the code size may increase
   exponentially, e.g. if function f calls g twice, and g calls h
   twice and h is inlined in g which is inlined in f (in either
   order) then there will be four copies of h's body in f.

   See also linear argument, unfold/fold.

   (1994-11-03)