Sepp is a short form of the German name Sebastian. It's often used as an affectionate nickname, similar to other diminutives like Seb or Baz. The name Sepp is particularly common in Austria and Bavaria, Germany, where it's often associated with warmth and familiarity due to its widespread use among family members and close friends.
Sepp is not a particularly popular name, with only five babies named Sepp born each year in 2012.