Overview
The word eroraibu combines "ero" with "raibu", from the English words erotic and live (adjective). Japanese speakers have used "raibu" as a noun to connote a live performance (such as an idol singer might perform for their fans). An eroraibu is the erotic form of that.
Apology
This is my first attempt at an article for pixiv. I'd never heard of this word before, so after failing to find an English explanation anywhere I searched for "raibu", then put two plus two together.