What does "saddleback" mean?

Saddleback: Anything saddle-backed; esp., a hill or ridge having a concave outline at the top.

Additional senses

  1. 2.(Zoöl.) (a) The harp seal. (b) The great blackbacked gull (Larus marinus). (c) The larva of a bombycid moth (Empretia stimulea) which has a large, bright green, saddle-shaped patch of color on the back.

Sources