What does "upscale" mean in the Anime world?

[UniSol GR77]

This is important.

For instance, Baldios episodes #30-32-33-34 are upscales and not native HD like the rest of the series and the movie.
Lupin Series 2 (Red Jacket) is upscale as well.
Cyborg 009, Saint Seya and other TOEI series are upscales.

What does that mean? What is the source? Do they use professional and expensive programs to "recreate" the lost visual informations and thus rendering the image an "artificial" HD version of itself? Does it work?

Just wondering. Thank you.