Honorific or familiar term for one's uncle. 伯父さん is used for an uncle older than one's parent, and 叔父さん for a younger uncle, though the kana form おじさん is common for both.
My uncle (older than my father) lives in Osaka.
Uncle, come visit us sometime.
Familiar term for a middle-aged or older man, often used by children or in casual address. Can be used vocatively. Usually written in kana or katakana.
An old man is playing shogi in the park.
Mister, is there a station near here?
manybar goatfish
A species of goatfish (Parupeneus multifasciatus). Usually written in katakana as オジサン.
The manybar goatfish is a fish that lives in tropical seas.
The old man from the neighborhood greets me every morning.
Excuse me, sir, may I sit here?