u[ser]::perms

File owner permissions. 

g[roup]::perms

File group permissions. 

o[ther]:perms

Permissions for users other than the file owner or members of file 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 might have write/execute permissions.

u[ser]:uid:perms

Permissions for a specific user. For uid, you can specify either a user name or a numeric UID.

g[roup]:gid:perms

Permissions for a specific group. For gid, you can specify either a group name or a numeric GID.