What does NVL stand for?

What does NVL stand for? I'm talking about the Oracle and Informix (perhaps some others too) function used to filter out non NULL values from query results (similar to COALESCE in other databases).

"Null Value Logic" according to http://www.abbreviations.com/term/157605, but most of the other references I have found support Phil's "Null Value" supposition. I haven't found a definitive origin.

StackExchange Database Administrators Q#16433, answer score: 10