What do you call this?

[aby]

What do you call the one on the corner that usually drain the water from the main tank to the sump and it has a comb-alike on top of it? (please see below image for more detail)

 

[JUNBUG361]

Corner overflow. Is this a trick question? Cuzz I'm not drunk enough yet
:celeb2::beer:

 

[aby]

Corner overflow. Is this a trick question? Cuzz I'm not drunk enough yet
:celeb2::beer:

No it's not a trick question. I am a total beginner in saltwater aquarium and I am not familiar with the aquarium equipment, terms, etc.