Structured Query Language.
"[A] widespread misconception is that 'SQL' is an initialism that
stands for 'Structured Query Language' - this is not the case.
"During the 1970s, a group at IBM's San Jose research center developed
a database system 'System R' based upon Codd's model. Structured
English Query Language ('SEQUEL') was designed to manipulate and
retrieve data stored in System R. The acronym SEQUEL was later
condensed to SQL due to a trademark dispute (the word 'SEQUEL' was held
as a trade mark by the Hawker-Siddeley aircraft company of the UK)...
"ANSI has declared that the official pronunciation for SQL is 'ess kyoo
ell', although many English-speaking database professionals still
pronounce it as sequel."
http://en.wikipedia.org/wiki/SQL