Originally used by sailors, it's not commonly heard outside of old nautical contexts or pirate stories. Avast! Secure the mainbrace before the storm hits!
Pro Tip 2/3
Used to Interrupt
It's a way to abruptly stop someone or something, much like shouting 'Stop!' or 'Wait!' Avast! That's the wrong direction!
Pro Tip 3/3
Archaic Usage
It's an old-fashioned term, so using it in everyday conversation might confuse people. Avast! No one speaks like that anymore.