when you catch a glimpse - (deliberately or not) of someone's online chat. Sometimes they have been discussing you. Usually in a bad way.
1. My sister Mary had been chatting to her bff and forgot to log
off when she went to the bathroom. I cheavesdropped and saw she had been dissing me!
2. At the net cafe I did a cheavesdrop on the guy next to me and saw his romantic conversation with his lover