SIU = Southern Illinois University, located in Carbondale, Illinois. Home of the Salukis!

S.I.U -Abbreviated form of "Slut it up" - A motto, a philosophy, a way of life.
Invented on the night of February 20th 2007, due to excessive amounts of alcohol, by the infamous two (who would later be known as Team S.I.U) K-a and Simpson.
Used in reference to the events of a big night out, a party, or in fact the entire schoolies period and so forth. Depending on the persons’ mood or disposition, this philosophy can form a pivotal role in one’s life, especially whilst youthful and/or attractive and/or intoxicated.
Usually S.I.U relates to hooking up with (preferably) a McHottie - or two, or more come to that - of the male species, but has on occasion, warranted the act be undertaken with a female.
S.I.U is used in this abbreviated format to disguise its true nature, especially around the parentals who may find the notion ‘promiscuous’ or immoral, and the males who are targeted (maintaining an innocent femininity, particularly magnetising and effective).
S.I.U can be used to convey the various stages of ‘hooking up’, all the bases and a home run are covered, depending on the person who is indeed S.I.U.
The term can be used in normal conversation, i.e. spoken, sung, chanted, communicated through sms especially when seeing a McHottie in nearby range, or over the internet i.e. msn and myspace.
The term is most prolific in the demographic of 18-20 year old females, from the Wazza region in Melbourne.

An acronym for "suck it up"

A man who's loved by everyone. He's remembered by his amazing muscles and his long luscious flowing hair. He loves to laugh and make others laugh as well. People are mesmerized by astonishing looks. Definitely a man deserves 10/10

Acronym for Special Investigation Unit for law enforcement/prosecutors and insurance compaines

Acronym for 'step it up' meaning for one to reach a new/higher level then previously on.

Commonly used in forums and online gaming.

a unit of measurement equalling 5'0"