[Haskell-beginners] definition of combinator

[Michael Mossey]

Although I can use libraries like Parsec, I don't really understand what a 
combinator is, theoretically. There is an article here

http://en.wikipedia.org/wiki/Combinator

with the statement "A combinator is a higher-order function that uses only 
function application and earlier defined combinators to define a result 
from its arguments."

Okay, so I believe a "higher-order function" is a function that takes 
function(s) as its argument(s). I don't know what "uses only function 
application" means. Application of what functions to what? Can someone give 
a concrete example that's simple?

Thanks,
Mike