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1.
MSS
A secluded cult of extraordinarily talented indivuals. The cult has been linked to conspiracies such as 'the 2 ratio' and is an open supporter of bolt action rifles, primarily the M40. It is rumoured that new recruits are put through a grulling initiation process at an anti-terrorist training facility in Venezuela. The definition of the abbreviation 'MSS' is a well guarded secret known only by the cults' leaders and most valued members.
'Ahh.. MSS are at the top of the leaderboard..... again'
'Why do MSS pwn us so bad?'
'That guy no-scoped like only an MSS could!'
by M40A1 Whore February 04, 2009
 
2.
MSS
MSS (Main Squeeze Security), n.

The security that comes with being someone's bottom bitch.

It provides one with the comfort of knowing that, even though your partner is out fucking other people, they'll always come home to you.

Also known as a Social Security Number for the polyamorous.
Person 1: "How do I know you aint just gonna up and leave me for some hoe?"

Person 2: "Relax girl, you got MSS"
by wellisntthisfunny October 23, 2010
 
3.
MSS
Midnight smoke session. usually referring to staying up late smoking weed, or waking up in the middle of the night to get high.
Man I'm tired from that late mss last nigh.
by Ex.Tc June 26, 2011
 
4.
Miss. Squish. Squirt. When doing a classy lady from behind, near ejaculation, one goes in for one last thurst and MISSES, squishing the phallus against her bum cheeks, causing the male to ejaculate into his own ocular region.
Jeremy suffered from M.S.S. and was so embarrassed that he never told his friends.
by butt diddlee May 03, 2010
 
5.
MSS
Multiple Semenation Syndrome. To semenate multiple times when ejaculating.
1: Wow that felt like you were firing a machine gun in my vagina.
2: Nope that was my penis. I have MSS.
1:Good. Because if that was a machine gun you would have ripped shit up.
by Captain Care Bear December 30, 2011
 
6.
MSS
Short for Mohammed Sayeed-al-Sahaf, former Iraqi Minister of information.
Did you see MSS on CNN? What an idiot!
by Performaman November 03, 2003