Two senses: (1) ordinary clapping/applauding (synonym
鼓掌 gǔzhǎng is more common in formal/audience contexts), and (2) the gesture of slapping palms together to seal a verbal agreement — like a Western handshake or 'high five on a deal'. Compare
击掌 (jīzhǎng), which leans more toward a celebratory high-five.