I search for solutions in this order: Past Code, Unreal Source, Wiki, BUF, groups.yahoo, google, screaming at monitor. – RegularX

From Unreal Wiki, The Unreal Engine Documentation Site

Object >> Primitive (native-only)

Package: 

Engine

Direct subclass:

Mesh

This class in other games:

U1, U2, U2XMP, UT, UT2003, UT2004

The base class for 3D primitives, like vertex meshes, static meshes or terrain.