Boom Operator
1. an assistant of the production sound mixer. The principal responsibility of the boom operator is microphone placement, sometimes using a “fishpole” with a microphone attached to the end and sometimes, when the situation permits, using a “boom” (often a Fisher boom) which is a more intricate and specialized piece of equipment that the operator stands on, and that allows precise control of the microphone at a much greater distance away from the actors. He or she will also attach wireless microphones to actors, celebrities and anyone whose voice requires recording.
The boom operator must decide where to place the boom microphone based on a combination of factors, including the location and projection of any dialogue, the frame position of the camera, the source of lighting (and hence shadows) and any unwanted noise sources.
Source: Wikipedia