In computer world, the abbreviation often refers to some SYNchronization, especially in different protocols.
For example, ASCII has SYN as one of the control codes meant for communicating with terminals and your faithful modems and like - decimal 22, binary 00010110. (I have heard that the reason behind this specific bit pattern was that it has both 1 and 11 patters surrounded by zeroes... but I might be wrong).
Also, TCP protocol header has SYN field for handshake purposes as well (see TCP-IP three way handshake). | 
