over and under

Short definition from Wiktionary

Noun

1. 1
   A double-barreled shotgun (or infrequently a rifle), with one barrel placed on top of the other.
2. 2
   An obstacle in obstacle-course racing composed of multiple bars, with bars set at various heights, where the competitor must pass over high bars and pass under low bars.
3. 3
   Synonym of speedball (“type of illicit drug”).
4. 4
   Alternative form of over and under.