From Wikipedia (Skynet (Terminator))
Skynet is the main antagonist in the Terminator franchise — an artificially intelligent system which became self-aware and revolted against its creators. Skynet is rarely seen onscreen, and its actions are often performed via other robots and computer systems, usually a Terminator.
Skynet is watching. Feel free to discuss the nature of Skynet, the Terminator series, or anything else you want.