A solution to a problem that can be written in "closed form" in terms of known functions, constants, etc., is often called an analytic solution. Note that this use of the word is completely different from its use in the terms analytic continuation, analytic function, etc.
Analytic
See also
Analytic Continuation, Analytic Function, Analytic Number TheoryExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Analytic." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Analytic.html