While both telesync and cam are illegal format, there is a distinct difference between cam and telesync. 

Cam movie releases is when someone is sitting in the theater and recording directly from their camera.  The sound unfortunately is also recording with the camera.  This leaves in laughter, often we’ll see people walk in front of the screen, etc.  Cam releases are usually the first formats to be released.

Telesync movies releases usually come after cam releases and is recording from the audio jack which is there for the hard of hearing people. Often, a telesync is filmed in an empty cinema or from the
projection booth with a professional camera which ends up giving us a much better picture
quality.

Image via DouG!!