STL (Standard Template Library)
Templates provide a way to make a generic implementation which would deal with any class (double, int, float, and also other user-written classes).
Writing templates is not easy if they are supposed to be general enough. Luckily, some smart people have collected the most wanted and most useful templates and bundled them into what’s known as the Standard Template Library.
One caveat: STL is a “standard”, but with the implementation, your mileage may vary. In a few months, hopefully all compilers will be smart enough to handle all of it.