Masquerade Tattoo, Inc. | Glossary of Terms

Gauge;

–noun
the thickness or diameter of various, usually thin, objects, as the thickness of sheet metal or the diameter of a wire or screw.

'Gauge' applies to the thickness of the individual pins that make up a tattoo needle as well as the diameter of the needle used for body piercing.

To 'Gauge' ones ears is a more recent popular term used to describe the stretching of a piercing using tapers and slowly incrementally replace body jewelry with larger gauges to increase the size of the hole it self..

[see this gauge chart jewelry.about.com]