What is surfs up meaning?

"Surf's up" is a slang expression in surfer culture that means the waves are good and it's a good time to go surfing. It's often used to announce to fellow surfers that it's time to hit the waves. The phrase originated in the 1960s and became popularized by the Beach Boys' hit song "Surfin' U.S.A." The term has since been adopted into mainstream culture and is used colloquially to mean that something exciting or fun is happening.