u[ser]::perms 

The owner's permissions. 

g[roup]::perms 

Permissions for the owner's group. 

o[ther]:perms 

Permissions for users other than the owner or members of the owner's group. 

m[ask]:perms 

The ACL mask. The mask entry indicates the maximum permissions allowed for users (other than the owner) and for groups. The mask is a quick way to change permissions on all the users and groups. 

For example, the mask:r-- mask entry indicates that users and groups cannot have more than read permissions, even though they may have write/execute permissions.

u[ser]:uid:perms

Permissions for a specific user. 

g[roup]:gid:perms

Permissions for a specific group.