Top Definition
Graduate Student Instructor. Terminology used at UC Berkeley.
My GSI was able to help me in the discussion portion of the class.
by Go Cal!!!! June 09, 2009
Synonym of SIF (secret internet fattie) for the Spanish Gorda Secreta de Internet.
"Hey Erdos, I believe this OkCupid profile is GSI compliant."

"Yeah, look at that strategic camera angle"
by MeherBaba April 24, 2007
GSI stands for G String Invaders also known as the IMEA (International Male Escorts of America) is an exclusive male escort assosiation founded by CEO Mr.Mandingo aka Adonis and Co founded by Mr.Tripod aka Pop Tent. The founders go by many names including The Lumber jacks, The Old Spicemen, The Wrecking Crew, The Demolition Crew, The Fire Crew, Nights of the 209, Adonis and Pop Tent, Mandingo and Tripod, and IMEA. They're slogan "The customer always CUMS first" is guaranteed. GSI is exclusive and is held to the best standards. Bestvdamn service you will ever get GUARANTEED.
Crystal: Omg so i orderd these guys called G.S.I. and they fucking wrecked my chasm and spooged all over me. They're slogan "The customer always CUMS first " wasn't a joke. I think im gonna call them again.

Nicole: Damn girl whats they're number??? I want to my fucking pussy filled that good too!
by Pito Gainer August 03, 2014
Is an acronym for the Greer Sucks Initiative. To show a webpage or product supports the initiative, put the following somewhere in the document:

This page is GSI Compliant
Jay> Man, did you see that transformer explode all over Greer's Accord?
Wes> Yup, I wonder why he parked under it?
Jay> I know why!
Wes> Why?
Jay> Greer Sucks!
by GsiCommish October 13, 2004
acronym for "Get Stuck In" or "Get Sexual Intercourse"
Sam: I'm away to talk to Amy

James: GSI dude
by JTJP March 16, 2007
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