A borefest is an event, a meeting, or a stretch of time that is very, very boring — so boring that people joke it is like a festival of boredom. It is a playful, informal word. You would not put it in a serious report or a school essay. People use it when they want to complain with a smile: a long speech with nothing new, a dry training day, a party where nobody talks. The ending -fest makes it sound like a big event built around one thing; here that one thing is being bored. You will hear it more from speakers who like jokey made-up compounds than in careful formal English. It is countable: What a borefest.

超無聊的活動、悶會（開玩笑的說法）