I thought maybe it would be worth seeing if there are any "authoritative" definitions online. Not really. Of the dozens I looked through, all said small and flat bottomed. Most said lightweight. Some (about half, give or take) said square bow and stern. Fewer said specifically aluminum, others said usually aluminum but other materials too, and a few (that seemed to be trying to be comprehensive) said aluminum, fiberglass, wood, or polyethylene. A very few talked about them riding over waves rather than cutting through them.
For what it's worth, I'd say the vast majority of these are no more authoritative than the people posting here, but it was worth seeing if there was anything.