An uncle—the male sibling of one's parent. Depending on age relative to the parent, kanji may distinguish 伯父 (older) and 叔父 (younger).
週末に叔父が遊びに来る。
My uncle is coming to visit this weekend.
伯父は海外で働いている。
My uncle (older than my parent) works abroad.
子どもたちはおじと一緒に公園で遊んだ。
The children played in the park with their uncle.