Oberst is a German Wehrmacht rank, at least in the Heer and Luftwaffe, above an Oberstleutnant but not quite a Generalmajor. It was equivalent to a Kapitän zur See in the Kriegsmarine (Navy), and a Standartenführer in the Waffen-SS. Also, in the Luftwaffe Technical Services, one of the equal rank was called a Flieger-Oberstabsingenieur instead. Oberst was commonly abbreviated as Ob or Obst.
An Oberst is basically equivalent to a full-bird Colonel in the United States Armed Forces (an O-6 on our pay-charts). The rank was represented by two pips on the senior officer shoulder boards.
You can see the entire rank structure and how Oberst fit into it at Wehrmacht Ranks.