In opera parlance, what is the difference between a diva and a prima donna?

Originally used in opera companies, "prima donna" is Italian for "first lady". The term was used to designate the leading female singer in the opera company, the person to whom the prime roles would be given. The prima donna was normally, but not necessarily, a soprano. The corresponding term for the male lead (almost always a tenor) is "primo uomo".

https://en.wikipedia.org/wiki/Prima_donna

A diva is a celebrated female singer. The term is used to describe a woman of outstanding talent in the world of opera, and by extension in theatre, cinema and popular music. The meaning of diva is closely related to that of "prima donna".

https://en.wikipedia.org/wiki/Diva