1. What is a denomination—specifically a Christian denomination?

Question

2. Which denominations are included in Christianity?

Answer 1

Here's the definition of "denomination" from American Heritage Dictionary in Dictionary.com.

"A large group of religious congregations united under a common faith and name and organized under a single administrative and legal hierarchy."

Check this site for a lengthy list of Christian denominations.

http://en.wikipedia.org/wiki/List_of_Christian_denominations

This site compares the major denominations in the U.S.

http://www.history.com/encyclopedia.do?articleId=227134