Residential - Generally all or a majority of single family sites. May or may not include duplexes, apartments and private roads.
Commercial - sites which are used by the general public - businesses, and may include duplexes, apartments etc, depending on the insurance company.
Industrial - self-explanatory - not routinely used by the general public. Factories, distribution centers etc.
Municipal - government owned or managed. Streets, highways, schools etc.
Individual insurance companies may have policies whereby some accounts of one type can be mixed with another. For instance, I had a written statement that I could plow commercial accounts on a Residential policy, providing the number of commercial accounts did not exceed the number of residential accounts. So technically, I could plow a shopping mall for every single family account. On the same policy - I got the ok to plow a library, although it was by definition a commercial site. Reason was the remoteness of the site. I showed them that it was in a rural area with no other public facility within five miles of the library.