1A professional — someone whose skill and experience in a field are high enough to be paid for it, as opposed to an amateur.
彼はサッカーのプロだ。
He is a professional soccer player.
プロの仕事は仕上がりが違う。
A professional's work turns out differently — the finish is better.
彼女はプロ並みの腕前だ。
She has skills comparable to a professional.
この仕事はプロに頼んだほうがいい。
It's better to ask a professional to do this job.
2Abbreviation of 'program' (プログラム). Once used in broadcasting jargon for a program or schedule, but this sense is essentially unused in modern Japanese — speakers now say プログラム or 番組 instead.
3Abbreviation of 'production' (プロダクション); refers to a talent agency or production company that entertainers belong to — still common as industry jargon.
彼は大手プロに所属している。
He belongs to a major talent agency.
あの新人は有名なプロからデビューした。
That newcomer debuted under a well-known talent agency.
4Abbreviation of 'proletarian'/'proletariat'; a term from pre-war socialist and communist discourse in Japan, essentially unused in contemporary Japanese.
5Abbreviation of 'propaganda'; nowadays speakers usually say プロパガンダ in full, so this abbreviated sense is rarely used.