Explanation
Virtual firewall rules for your VCN. Your VCN comes with a default security list, and you can add more.
These security lists provide ingress andegress rules that specify the types of traffic allowed in and out of the instances. You can choose whether a given rule is stateful or stateless. Security list rules must be set up so that clients can connect to file system mount targets. For more information about how security lists work in Oracle Cloud Infrastructure, see Security Lists in the Networking documentation. For information about setting up specific security list rules required for mount target traffic, see Configuring VCN Security List Rules for File Storage. About Security explains how security lists interact with other types of security in your file system.
https://docs.cloud.oracle.com/iaas/Content/File/Concepts/filestorageoverview.htm