Refers to a man who is very particular about his appearance and fashion, often with a refined or elegant style. The term can carry a slightly old-fashioned or ironic nuance, similar to 'dandy' or 'fop' in English.
He's always a dandy who wears his suits well.
That actor is known as a dandy.
Loanword from English 'dandy' + 'man', likely entering Japanese in the late 20th century as a term for a fashion-conscious man.