What does opus mean?

[loganorigami]

Why do some people ( like Robert Lang ) put opus (number) after pictures of their models.

[Menschenfeind]

It's latin for "work" (Magnum Opus = Greatest work)
Some musicians also did it, like Chopin.

[HankSimon]

.... And, so Robert Lang labels his Origami works of art with opus numbers to make it much easier to organize and track them. Just as Lang has 'copied' the music world, some young origami artist have copied Lang in this practice with their own set of opus numbers.