Champerty

n.
  1. Partnership in power; equal share of authority.
  2. (Law) The prosecution or defense of a suit, whether by furnishing money or personal services, by one who has no legitimate concern therein, in consideration of an agreement that he shall receive, in the event of success, a share of the matter in suit; maintenance with the addition of an agreement to divide the thing in suit. See Maintenance.

By many authorities champerty is defined as an agreement of this nature. From early times the offence of champerty has been forbidden and punishable.