1. traffic accidents involving multiple vehicles that crash into each other in sequence
2. accumulations or buildups of things in a heap or mass

Examples

• The icy highway caused several pileups during the morning commute.
• A massive pileup involving twelve cars blocked traffic for hours.
• Fog contributed to multiple pileups on the interstate.
• The snowstorm led to dangerous pileups throughout the city.
• There were pileups of paperwork on every desk in the office.
• The strong winds created pileups of leaves in the corners of the yard.
• Pileups of dirty laundry covered the bedroom floor.