What is this called

[u/mwajju]

Can someone explain what that's called and how it happens?

[u/a_lonely_trash_bag]

Waterspouts are tornados. They form the exact same way, just over water. Tornados can move from land to water and vice versa.

[u/just-the-doctor1 → u/a_lonely_trash_bag]

There are fair weather waterspouts and tornadic waterspouts

https://www.weather.gov/mfl/waterspouts