The Collaborative International Dictionary of English v.0.48:

Tangelo \Tan"ge*lo\ (t[a^]n"j[-e]*l[=o]), n. [Tangerine +
   pomelo.]
   A hybrid between the tangerine orange and the grapefruit, or
   pomelo; also, the fruit.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

tangelo
    n 1: hybrid between grapefruit and mandarin orange; cultivated
         especially in Florida [syn: tangelo, tangelo tree,
         ugli fruit, Citrus tangelo]
    2: large sweet juicy hybrid between tangerine and grapefruit
       having a thick wrinkled skin [syn: tangelo, ugli, ugli
       fruit]