UVW TagBasic Tag
The UVW tags contain the UVW coordinates (they define which region of a texture should be displayed on a given polygon; UVW mapping must be selected as projection type in the Texture tag).
UVW tags will automatically be created when parametric primitives (cubes, torus, etc.) or objects that are used to create geometry (sweep object, etc.) are made polygonal.
Of course you can also edit and create UV coordinates manually, which is often necessary when painting more complex objects. Various tools for doing so can be found in the BodyPaint 3D Edit UV menu.
An object can contain any number of UVW tags. A Texture tag will use the UVW tag that lies closest to its right in the Object Manager.