From Jargon File (4.3.1, 29 Jun 2001) :
deprecated adj. Said of a program or feature that is considered
obsolescent and in the process of being phased out, usually in favor of
a specified replacement. Deprecated features can, unfortunately, linger
on for many years. This term appears with distressing frequency in
standards documents when the committees writing the documents realize
that large amounts of extant (and presumably happily working) code
depend on the feature(s) that have passed out of favor. See also dusty
deck.
[Usage note: don't confuse this word with `depreciate', or the verb
form `deprecate' with `depreciated`. They are different words; see any
dictionary for discussion.]