Other people have explained that it is a game jam event.
"Ludum dare" is Latin for "to give a game" or "game giving".
Big online Game Jam (Hackathon for games). Some Notable games like Broforce and Hollow Knight started there.
Inscryption, too. I didn't know it started as an LD game until after I played it, and it was great to see how much of the atmosphere and mechanics were already there in the LD version [1].