Bake maps should be refered to texture baking. It can be used for a variety of things to simplify a material. An example would be a terrain texture that uses 3-4 tiling textures and they are all layered together using opacity maps. You could use render to texture to take that, and take a picture of the material and then save it to 1 bitmap that you can use in your scene, or a game level. You can refer to the render to texture documentation in the map help file, it should explain alot of stuff... you can also google up "Render to Texture 3dsmax" and you should come up with some tutorials and more information. Theres also light baking as well which some renderers and applications let you to do. It will basically calculate a high quality lighting solution, like global illumination, and it will combine the calculated lighting into the actual diffuse texture map. After thats done, you do not need to recalculate the lighting for every frame, and it will drastically help when rendering animations and camera flythroughs. Again, there are some useful application for games as well.