1. To kiss passionately. A long deep probing kiss, usually involving tongue, preferably only ending when bruised lips and tongue cramps occur.
Australian slang term, gradually being taken over by European term snog, and more popularly refered to as kissing, or making out. Commonly seen as being derived from the word passion, however it's origins are more likely connected to the meaning described directly below (2.). Made psuedo-popular in the 90's by intensely irritating, and amazingly cheesy pop song by Kate Cebrano.
2. To have a crush on somebody. To lust after them. i.e. To have a pash on somebody.
A slightly older, not so common british slang term, which was used by young girls in particular to express feelings they had for a male (whether that be a boy of similar age, or a movie star). Originally derived from the meaning which trusty Webster sheds light upon below. 'It's got that ring of 1940's girls' storybooks' - heyoka