IAtionary: Juniority

Jun-ior-i-ty [joon-YAWR-i-tee] n.

1. the state or condition of being older than the sophomores and freshmen, but not older than the seniors
2. the juniors' equivalent of seniority; he used his juniority to cut in front of the 10th graders in line, but he was not able to pass the 12th graders

Also:
Sopho-mor-i-ty [sof-MAWR-i-tee] n.

1. the state or condition of being older than the freshmen, but not older than the juniors or seniors
2. the sophomores' equivalent of juniority