Cross-processing, briefly, is a photographic technique where (usually) slide film (E6) is processed in the set of chemicals usually used to process print film (C41). (Less common is cross-processing in the other direction -- print film processed in slide film chemicals).

The result is images with oddly skewed colors and increased contrast and saturation. Image contrast is usually high with blown-out highlights, while the shadows tend toward dense shades of blue. Reds tend to be magenta, lips almost purple, and highlights normally have a yellow-green color cast.

All my Cross processing are directly produced from RAW by Adobe LightRoom 1.0 (registered version, not beta), without any PhotoShop manipulation.