Definition of branch off phrasal verb from the Oxford Advanced Learner's Dictionary

Phrasal Verbs
  1. 1(of a road or river) to be joined to another road or river but lead in a different direction Just after the lake, the path branches off to the right. See related entries: Features of roads, Rivers and lakes
  2. 2(of a person) to leave a road or path and travel in a different direction
See the Oxford Advanced American Dictionary entry: branch off