c++ syntax question

Hi /prog
When working with some other C++ libraries, I often see a class declaration like so:

class LIBRARYNAME_API ClassName
{};

Could someone please explain what the "LIBRARYNAME_API" part actually does?

>>2
C++ sucks. Your english sucks. You suck. Man, I tell you, this is the kind of shit that makes me want to stop working as a computer programmer, and instead, work as a gay tranny prostitute in the castro.