Refers to an artistic or literary pseudonym, especially one used by calligraphers, painters, or writers. More formal than ペンネーム.
He publishes his works under a pen name.
As a calligrapher, one has a pen name.
雅号 is a traditional Japanese-style pen name often used by classical writers, painters, or poets, whereas ペンネーム is the modern, casual term used for any writer.
From 雅 (elegant, refined) and 号 (name, title). The term has been used historically for the artistic names adopted by practitioners of traditional arts.