Global System for Mobile communications.

The most common digital cellular system in the world. GSM is used all over Europe, plus many countries in the Middle East, Asia, Africa, South America, Australia, and North America. GSM's air interface is based on narrowband TDMA technology, where available frequency bands are divided into time slots, with each user having access to one time slot at regular intervals. Narrow band TDMA allows eight simultaneous communications on a single radio multiplexor and is designed to support 16 half-rate channels. GSM also is the only technology that provides incoming and outgoing data services, such as email, fax, and internet surfing. GSM makes use of a SIM card that allows memory portability between dumb GSM phones.
The GSM system allowed for both internet surfing and digital voice communications over 1900 MHz radio networks.
by IrishrepublicanArmy January 24, 2004
Gender and Sexuality Minority. A more encompassing version of LGBT or the gay community.
V: Who's she going out with, again?
W: Shelly. They're GSMs.
by Sheenangua June 30, 2011
Game Set Match. Generally used to mark the end of an argument or discussion.
Gertrude: "I believe that I am the most awesome person in the world."

Jack: "You stole a small child last week from the grocery market. That is totally not awesome. GSM"
by JawesomeSauceisCrabs November 16, 2011
me vs Jason in bowling? He has no chance. It is GSM.
by K-rose August 18, 2005
"Gay-Straight Man"

When "metro" just doesn't quite do it for you.

A man almost certainly gay, yet still likes to have sexual intercourses with many women.
That GSM is so DTF girls.
by snowfender September 8, 2010
Short for "Get some more". Use while texting
I just plowed a fat chick. So good I'm going to gsm that shit tonight!!!!!
by Lomo October 5, 2014
Dan: What you do last night pal?

Cal: Drank tinnies, was fun.

Dan: GSM
by jizzyjez September 12, 2013