It means uncle, although in anime character regularly use it in its less formal form where it functions more as "mister" or "sir." It's just an informal, but not necessarily rude, way to refer to an older man than yourself that you're unfamiliar with.

That's all I wanted to get clear. Most definitions stop at uncle and barely explain the secondary, and probably more common, use for it. "Ojisan" always means "sir/mister" unless they're actually they're uncle.
"You dropped your wallet, Ojisan" = "You dropped your wallet, mister/sir."
by i8toast7 November 16, 2018
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Japanese for Uncle. Not to be confused with Ojiisan, which means Grandpa.
My Ojisan is going bald.
My Ojiisan is going short.
by Spazmatik Illusion January 17, 2006
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Ojisan literally means Uncle in Japanese.

Can also be used as a slightly impolite way to address a middle aged man, similar to the English "Mister".
My Ojisan is visiting from Osaka tomorrow.

Excuse me Ojisan, which train goes to Kyoto?

Hey Ojisan, keep your hands off my girl.
by DicemanLucky7 July 10, 2008
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The name for an old man.
We call Bryson Ojisan because hes old.
by Kalihi Lover October 29, 2015
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Old-fashioned people lack of knowledge for IT tools (SNS is exceptional) and gender equality.
If you have a/some ojisan in your team, your work will be more than double.
Yeah he is exactly Ojisan so that he will not try to understand what she is trying to say.
by HampyWampy July 1, 2020
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