In music, wah-wah is used to describe the sound produced by covering and uncovering the open end of a brass instrument. This sound can also be produced electronically, especially when playing the electric guitar. He played some wah-wah guitar
Used within the British Army in response to an answer to an obvious question. This is a question that you have set the other person up to answer. Can become quite frustrating as you become paranoid answering any question in case it is a Wah!