This explanation from Wikipedia might be a little more… helpful… than a URL that just points to Google:
"In 3D computer graphics texture filtering, MIP maps (also mipmaps) are pre-calculated, optimized collections of bitmap images that accompany a main texture, intended to increase rendering speed and reduce artifacts. They are widely used in 3D computer games, flight simulators and other 3D imaging systems. The technique is known as mipmapping. The letters “MIP” in the name are an acronym of the Latin phrase multum in parvo, meaning “much in a small space”. They need more space in memory although they form the basis of wavelet compression.
“Each bitmap image of the mipmap set is a version of the main texture, but at a certain reduced level of detail. Although the main texture would still be used when the view is sufficient to render it in full detail, the renderer will switch to a suitable mipmap image […] when the texture is viewed from a distance or at a small size. Rendering speed increases since the number of texture pixels (“texels”) being processed can be much lower than with simple textures. Artifacts are reduced since the mipmap images are effectively already anti-aliased, taking some of the burden off the real-time renderer. Scaling down and up is made more efficient with mipmaps as well.”