An algorithm, as a concept, is an object which encapsulates a generic algorithm.
In generic programming, it is often desirable to parametrize an algorithm
by sub-algorithms. For example, the std::sort() algorithm in the C++
Standard Library takes in an object which defines the ordering to use.
Compared to a usual functor, an algorithm object is different in that
usually the functor's operator() is not a function template. For
example, while normally you would pass a std::less<int>() to the
std::sort(), with algorithm objects you would pass a LessThan(),
which encapsulates a less-than comparison for all types.