Siphon flush-to-floor shower functionality (old building)

Hello everyone,

I am completely new here, so please forgive me if anything is unclear :D

Some context: I have a small old apartment in Berlin with a very old bathroom, where the shower drain regularly causes me problems.

The shower is flush with the floor and the water flows into a siphon in the floor - not in the shower itself. This type of siphon (see sketch) is honestly completely unfamiliar to me. Can someone briefly explain what it is called exactly or how it works?

Best regards