[from the default flavor of ice cream in the U.S.] Ordinary
flavor, standard. When used of food, very often
does not mean that the food is flavored with vanilla extract! For example,
vanilla wonton soup means ordinary
wonton soup, as opposed to hot-and-sour wonton soup. Applied to hardware
and software, as in Vanilla Version 7 Unix can't run on a vanilla
11/34.
Also used to orthogonalize chip nomenclature; for instance,
a 74V00 means what TI calls a 7400, as distinct from a 74LS00, etc. This
word differs from canonical in that the latter means
‘default’, whereas vanilla simply means ‘ordinary’.
For example, when hackers go on a great-wall,
hot-and-sour soup is the canonical soup to get
(because that is what most of them usually order) even though it isn't the
vanilla (wonton) soup.