As defined on the 9Korea website, “Ahjussi (아저씨) means 'middle-aged man' or 'married man' in Korean. Ahjussi can be used when calling an unfamiliar grown man; it is equivalent of calling a man 'Mister'.” Other sources also state is means “uncle”. This term can also be romanized as ajusshi or ajeosshi.

Other sources go further in the characterization of the term, such as the Our Man in Korea blog: "the male equivalent of the ajumma, the ajosshi is best characterised as a middle-aged businessman/office worker, often called a salaryman in Korea. The stereotypical ajosshi wears a grey or black suit with a tie – the suit is often made of a shiny polyester-like fabric and the tie may have sparkly silver bits in it. His natural environments are the office – where he works steadily but slowly all day and half the night – and the restaurant/pub, where he goes after work. The ajosshi can be grumpy, but he is often an affable bloke, especially when red-faced from drinking. He can sometimes be found face down in a pool of vomit, or else stumbling home at 6am on a Wednesday ready to work another 11 hour day. Again, not every middle-aged Korean man resembles this fellow."

An interesting phenomenon related to this word is the rise of a group known as the “ahjussi fans” (or uncle fans). K-pop groups are usually marketed with a younger audience in mind. However, a considerable amount of older men (both in Korea and in other places) have come to admit their love for k-pop. One group that has become particularly associated with ahjussi fans is Crayon Pop, whose quirky songs (such as Bar Bar Bar and Dancing Queen) and outfits have attracted the attention of many of such fans.