Mike, Ring is the RED wire. Tip is the GREEN wire of most standard
phone lines. They two constitute the two wires most often used for
voice telephone (the two live lines). They are the two innermost
connectors of an RJ-11 phone jack.

Another way of telling is that if you measure voltage from RED to
GREEN (ring to tip. tip/green being at ground potential of the
voltmeter), it should read -48 volts in the on-hook no-ring position).
I am 98% sure it's -48 V and not +48 volts. Doesn't hurt a phone too
much if they're reversed, it's just bad if one happens to somehow get
grounded to earth ground elsewhere).

Additionally, when off-hook, the voltage drops to about -4 to -9 Volts
DC. I think it is supposed to correspond to a 36 to 40 mA current
loop. And lastly, when ringing, the two wires develop an AC potential
of about 80 V p-p at 20 to 30 Hz across them (where you get the
electromechanical old fashioned bell ringer from).