An Access Control List (ACL) contains rules that grant or deny access to certain digital environments. There are two types of ACLs:
Filesystem ACLs - filter access to files and/or directories. Filesystem ACLs tell operating systems which users can access the system, and what privileges the users are allowed.
Networking ACLs - filter access to the network. Networking ACLs tell routers and switches which type of traffic can access the network, and which activity is allowed.