Sen Ni Sen
先二先 (sen ni sen) is a Japanese go term describing the handicap in a series of matches between two players - like a jubango, where one player takes Black in two games out of three and a two stone handicap in the other game. For more information on professional handicaps in the days before komi go, see Match Handicap System.
In the older system of pro handicapping, this was considered correct for players three dan levels apart. 
 On average, sen-ni-sen gives Black a 5/6 move's advantage.