This is a pretty good video abut the subject: https://www.youtube.com/watch?v=aYtXBUS_kwY

"Mosquito" just means buzzy and lacking clarity.

In the video, he's using good quality gear and is a pretty good player, so even when he does everything wrong it doesn't sound as bad as this problem can sound. Then again, his "good" example is still too distorted to record well even for the style of music he's playing (metal uses much more distortion than any other genre), and if I were recording him, I'd be begging him to take it down a couple more notches.

Over-distorted, i. e., buzzy, like a mosquito.