Ingress filtering is a method used in network security to ensure that incoming packets are allowed or blocked based on a set of security rules.
This type of filtering is often implemented at the boundaries of networks to prevent unwanted or harmful traffic from entering a more secure internal network.
The term "ingress" refers to traffic that is entering a network boundary, whereas "egress" refers to traffic exiting a network.
Reference
Cisco Networking Academy Program: Network Security.
"Understanding Ingress and Egress Filtering," Network Security Guidelines, TechNet.