Vent, clean-out or...?

This is probably common knowledge, and I’m going to feel pretty stupid for asking this, but can someone please tell me exactly what this is. I’m thinking it’s some kind of clean-out covered with a metal plate, but every time I see these things there’s never any kind of plumbing near it on the inside wall, so I’m not positive what it is.

Thanks for any responses.

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You got it clean out cover.
Regards Bill

…or an access cover to something. Kinda weird to see it on the outside of the house.

Clean out for what? It’s under a window, so I don’t think is for a fireplace pit. Did you have something else in particular in mind?

sewer cleanout cover:

Oh, OK… I ain’t never saw one like that. Sewer clean out…

I’ve never observed one being used for a resi application. They’re in frequent use in commercial occupancies.

That explains why I’ve not seen one, I suppose.

Thanks for your responses. I see them quite often here in newer homes - usually more than one to a house. I didn’t know what else they could be except some kind of vent, but I just wasn’t sure.