There are a bunch of different maps actually and they're not limited to shading, you can control dynamic some simulations etc. I mean there are the typical maps like color, transparency, bump, displacement, specular but you can create maps for many other channels you'd like to control.

As far as getting to know normal maps a little better you can check its wiki page. I wouldn't say specular maps make highlights stronger, I'd say it enables the specularity to vary across the surface.