It's thrown around pretty loosely these days, but the term originally
referred to the aluminum-copper alloys developed in Germany around WWI,
which were given the name Duralumin. They were similar to today's 2024.
Then other precipitation-hardening grades were developed, and the term
today usually refers to 2024, 7075, and maybe a couple of other grades in
the 2000- and 7000 Series.

But it's become a marketing term, like "billet," so you can't count on it
referring to a particular grade anymore.

Ed
My son had a project where he built jet engine hangers for a new, more
powerful C7 military transport jet engine. The billets for this project were
4" thick by 48" by 144". "The Kid" only knew it was a special military grade
AL alloy. He brought home a pile of scrap from this job. Any way to guess
what this stuff is and its properties? I've got a few hundred lbs.

Karl