In the manual’s entry for the Math node, the Fraction operation is a link to a Wikipedia entry about Rational Functions, which seems too complex an answer (if any, at all), given that this operation is part of the set of rounding ones. Surely a more straightforward one is possible.

I’m studying a material that uses this node and so I need to know what it does.

(The description in the compositing nodes section suffers from the same problem)