Mids and Highs — these two differnt types of drivers handle the upper portion of the frequency range.
Their official names are mid-range drivers and tweeters.
Mids are a very big part of doing an after-market install and they are usually the quickest HOOK UP project you can do. Most often it just involves changing out the existing door speakers that your car came with. A straight swap. Some mids are classified as mid-bass drivers because they can go a bit lower into the upper ranges of what a subwoofer can do.
Tweeters are just that, the highs – think that crystal glass breaking type of shriek. Actually highs start much lower on the frequency curve.
There is a driver called a Co-Axial. This beautiful product takes a mid-driver and mounts a tweeter to it.