When you don't know what a word means, the best place to start looking is usually a dictionary. For example, Merriam-Webster's definition 3:

  a small or inferior remnant or offshoot; especially :  a group 
  (as a parliament) carrying on in the name of the original body 
  after the departure or expulsion of a large number of its
  members 

http://www.merriam-webster.com/dictionary/rump