P0138 Error Code

After receiving a P0138 code on my 2001 Ram 1500 4X4 I did some searching on the web to find that this indicates an O2 sensor high voltage bank 1 sensor 2....My question is what the hell does that mean? does it indicate that the sensor has gone bad or that the sensor is recieving a high voltage from a problem somewhere else? Also...where is "bank 1 sensor 2" ? is this before the cat converter or after? When pricing it I was also asked whether it was the left or the right...I can only find sensors on the passenger side...Am I missing something here? Thanks in advance for any help and advice.

bank one sensor one is after the cat and the side that has the #1 cylinder...possible a bad sensor, bad cat, exhaust leak, or bad wiring

Thanks for your reply..Just to confirm my code indicates bank1 sensor 2, in your reply you said bank 1 sensor 1 is after the cat...Am I looking before or after the cat?