What's up?
American SlangDefinition
Informal greeting asking how someone is or what’s happening; often used as a casual “hello.”
Examples
"'What's up?' he said as he walked into the room and high-fived his friend."
"'Hey, what's up?' Mia called across the hallway as she spotted her old classmate."
"I bumped into my neighbor at the mailbox and said, 'What's up?'"