The third degree of the everlasting sexual bases metaphor. The best way to remember them is of course, the four "F"s. French, Feel, Finger, Fuck.
With his finger in Jenny's twat, he knew he had reached the coveted third base.
by rarmeister January 18, 2004
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The third base before home plate in baseball you damn perverts.
Jacki Robinson advanced to thrid from second after Duke Snider's single to centerfield.
by Paulness May 27, 2005
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The orignal definition was touching, feeling, and assumedly handjobs. But now that society has become so desensitized to the intimacy of sexual intersourse, what with children giving birth at 11, 12, 13, left and right, third base has now been shunted up to second and the acts of fellatio, cunnilungus, and on occasion even anal sex, which have been traditionally associated with full-on sexual intercourse (i.e. making it home or scoring) have been placed on third base in order to enable today's alienated and cynical youth to give blowjobs and eat out pussy to their heart's content.
Did you hear about Wilson? He got to third base and busted ALL OVER her face!
by John is awesome November 14, 2005
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Controversially debated, but the modern accepted definition of 'Third Base' is both Fellatio and Cunnilingus.

Fellatio being oral sex performed on a male, involves a penis being placed into ones mouth, commonly known as a headjob, sucking off or a blowjob, although one generally does not blow when performing.

Cunnilingus being oral sex performed on a female, involves a tongue entering a vagina, commonly known as licking out and eating out.
Late Tuesday night, Mike drove Jen to make out point in his newly imported supra, once there Mike managed to reach third base for the first time with Jen when Mike licked Jen's vagina. Jen had never given anyone a blowjob before and decided she would perform one on Mike the same night. That night Mike and Jen reached 3rd base both ways.
by ambulance_x February 3, 2007
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Getting to third base is the most ambiguous stage of high-school heterosexual interaction. The definition really depends on how far the boy goes: is it an intermediate stage followed by going all the way, or is it the final stage of making out? (everything that follows is from the boy's perspective) When I was a kid (mid-70s) it meant groping skin-to-skin instead of through the clothes. Today it's gone farther: "getting to third" implies that you eventually squirted; "I got as far as third" means that you didn't do it inside her (hand job, blow job, dry-hump, just lose it while making out, etc.). If you go all the way, it doesn't really matter when you got to third.
"How far did you go?"
"Third base, dude! She wouldn't drop her panties, but we kept at it until I spooged my boxers."
by e-boy February 19, 2007
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