fellatio; blow job
Loanword from English; used in both neutral and casual contexts. The gloss 'blow job' is more colloquial.
彼女は彼にフェラチオをした。
She gave him a blow job.
フェラチオ is the neutral clinical term for fellatio, while 尺八 is crude slang for the same act, evoking the shape of the blown instrument.
フェラチオ is the full, more clinical-sounding form, while フェラ is the casual abbreviation used in informal speech.
Borrowed from English 'fellatio'.