WordNet (r) 3.0 (2006):

Velveeta
    n 1: trademark: soft processed American cheese

The Jargon File (version 4.4.7, 29 Dec 2003):

velveeta
 n.

    [Usenet: by analogy with spam. The trade name Velveeta is attached in the
    U.S. to a particularly nasty processed-cheese spread.] Also knows as ECP;
    a message that is excessively cross-posted, as opposed to spam which is
    too frequently posted. This term is widely recognized but not commonly
    used; most people refer to both kinds of abuse as spam. Compare jello.