An Autonomous System Number (ASN) is a unique identifier assigned to a collection of IP addresses managed by a single organization, such as an internet service provider or large company. ASNs are used in internet routing to distinguish different networks and help direct data efficiently across the global internet. By identifying the origin or destination of internet traffic, ASNs play a crucial role in network management, security, and troubleshooting. They enable organizations to exchange routing information with other networks, ensuring reliable and secure data transmission.