帰宅部 is a classic and well-known Japanese slang that literarily means a go-home “club”. People use this term to indicate that they don’t belong to any club at school while highlighting the fact that they are still a part of the group of people who opt not to join any club. Although it may sound like a joke term or something, it’s used commonly and naturally among students to describe such status.
幽霊部員 (ゆうれいぶいん) literally means “a ghost member at a school club” and describes members at a club who seldom appear in its events or activities.
部活 (Bukatsu) Culture in Japan
In Japan, most people join 部活 (bukatsu: a club) in junior high school and high school. There are roughly two types of them: 運動部 (うんどうぶ; sports clubs) and 文化部 (ぶんかぶ; arts/non-sports clubs). Popular sports clubs in Japan include baseball, soccer and basketball clubs, and they are typically very serious and strict. For instance, you usually have mandatory practices 5 or 6 days a week after school, and some clubs further require or ‘recommend’ you do 朝練 (あされん, morning practice) before a class starts. The social hierarchy in those clubs (especially in very strong and competitive ones) tends to be very strict as well, and you ought to be very polite to your coach and senpai (older students) using keigo (honorific language). Sometimes, some clubs are penalised for the abuse of power in the team, including the coach’s violence toward the students and senpai’s bullying of kohai (younger students). Some people argue that those extreme bukatsu cultures are anachronistic and promote blind obedience to the leaders or authorities.
On the other hand, non-sports clubs (i.e. 文化部) tend to be more casual and relaxed, although some clubs, especially 吹奏楽部 (すいそうがくぶ; brass band club) can be as strict as sports ones depending on a school.
帰宅部 consists of two parts 帰宅（きたく） meaning ‘go/come home’ and 部 (ぶ) meaning ‘club’. The first word 帰宅 is usually used as a suru-verb, ‘帰宅する’.
Because I belonged to 帰宅部 (‘a going-home club’) at high school, I would read a lot of manga after school.
Synonyms in English: not belong to any club at school
Related Words and Phrases: 帰宅する (go home), 部活 (club at school)