An omen is an event or happening that you take as sign of something to come. It’s believed to be a bad omen if a black cat crosses your path or if it rains on your wedding day.
Omens generally get a bad rap — that's probably because a lot of them predict bad stuff, at least according to superstition. But the interpretation of omens really depends on the country and culture. What's considered an ominous sign in one place might mean a lifetime of good luck somewhere else. Oscar Wilde once wrote that, “There is no such thing as an omen. Destiny does not send us heralds. She is too wise or too cruel for that.”