Ian_Lang:
Yes you are right in thinking that the centre is the output; it's commonly known as the wiper. But there is a caveat- potentiometers come with a logarithmic OR a linear track. If it's a volume control, it's probably the latter.
You mean "the former"...
Log potentiometers are also known as "audio taper" pots (vs "linear taper" pots); thus, any time you are dealing with audio signals (ie, a volume control, for example), it is likely to be a logarithmic/audio taper potentiometer.