Olsen_Morten_TheUltimateTrim.pdf
See Normal Edge Decals for an expansion on Trim Sheets by Leonardo Iezzi.
Trim sheets are special textures designed similar to a texture atlas. That is, they contain specific areas for specific details. The difference though is that instead of unwrapping the model and then designing the texture to fit the model, you design the texture and then unwrap the model to fit the texture. This is a useful technique for reducing performance (draw calls) requirements and is often used for environmental pieces. For a GDC talk regarding the use of Trim Textures in the game Sunset Overdrive by Morten Olsen (Insomniac Games), please see the link below.