I think K Gopalakrishnan has explained it in his Oracle Wait Interface, Oracle Press 2004 http://www.amazon.com/exec/obidos/tg/detail/-/007222729X/
Chapter 8 talked about it.
Oracle added alot of granularity to the 10g wait interface, but the documentation seems to be lacking. I tried googling, google groups, metalink, and otn and I can't really find any detail on this wait:
enq: SQ - contention
Looks like some kind of share lock contention(if I am reading it). I saw a vague reference in some powerpoint slides to ITL waits.
I opened a TAR, but sometimes it takes a while to get a response. Does Oracle document the new waits anywhere?
-- Yao Yongping Learning Oracle, UNIX/Linux... Love Reading, Classical Music, Philosophy, Economics etc. Blog: http://spaces.msn.com/yaoyp/