The "group" (really a Security Principal) Authenticated Users is a collection of users and computers which authenticate to the domain. From "Well-known security identifiers in Windows operating systems":
Name: Authenticated Users
Description: A group that includes all users whose identities were authenticated when they logged on. Membership is controlled by the operating system.
Security filtering can be used to apply [or prevent application of] policies to specific groups of users/computers. Typically you link a GPO within an OU and the policy applies to all users/computers within this OU. With filtering you can say: "apply this policy to only users in these groups within this OU".
When a policy's Security Filter is Authenticated Users is means the policy will apply to all users/computers which have authenticated to the domain. Of course, barring loop-back processing enabled, Computer Configuration settings will only apply to computer objects and User Configuration settings will only apply to user objects.