TITLE: What's difference between 'functional' and 'function'?
QUESTION [6 upvotes]: Hi, I want to know difference that between 'functional' and 'function'.
Of course, in Wikipedia, http://en.wikipedia.org/wiki/Functional_(mathematics), there is many texts.
But what's the simple answer for this question? ;-)

REPLY [3 votes]: No difference really, just convention.
A functional normally acts on other functions, whereas a function normally acts on some underlying vector space or field.  But this is not always true.