AWG is a standardized system used in US and Canada to organize the round wires used as current conductors (electrical cables).
The AWG system is also used to specify dimensions of jewels for body piercing.
The AWG increases with the reducing of the wire diameter because initially was related to the number of passages of wire drawing required to obtain the desired diameter, more passages correspond to a lower diameter, normally the greatest AWG value used is 44.
AWG 0 means no wire drawing but you could find also bigger wires indicated in different ways, for instance:
For details: American wire gauge on WikipediA