Question

What is overhead? Are there multiple types of overhead, or only one? What are some examples?

Answer 1

The business meaning of overhead cost explains it best. From Wikipedia:

The term overhead is usually used to
group expenses that are necessary to
the continued functioning of the
business, but cannot be immediately
associated with the products/services
being offered1 (e.g. do not directly
generate profits).

Overhead is a “cost” you will incur to be able to perform an operation; you need to “invest” some resource to perform the operation in question.