First base: making out (french kissing)
Second base: feeling up under or over clothes
Third base: hand jobs and fingering
(3.5: oral sex)
Home run: sex, (including anal)

A term used to reference cannabis/marijuana/weed.

Something all of which are belong to us.

Despite what most people believe, "Base" doesn't refer to any form of Speed or Meth. Base refers to Crack Cocaine, which is the FreeBASE form of Cocaine, hence the name, "Base".

A substance made up of about 60% amphetamine.
In contrast to speed, which is made up of about 5% amphetamine.

Often methamphetamine is defined as base: "a purer form of speed".
Methamphetamine is a completely different chemical, with different effects. Base is the same chemical as speed, just in much higher concentrations.
Usually has a different effect to speed, as the higher dosage doesn't just mean fuller effects, but whole new ones as well.

NB: both amphetamine and methamphetamine have absolutely NOTHING to do with 2,3 methylenedioxymethamphetamine (ecstasy), despite the uneducated and ill-informed ramblings of the DEA.

Morally low, shallow and low-brow

A pure and potent form of amphetamine, comes in a crystaline lump rather than a powder (although is normally cut before use).