Each file and directory has permissions associated with it. The first group represents the owner permissions on the file, the second group represents the group permissions on the file, and the third group represents the world permissions on the file. The owner is the user owning the file. Everyone with the same group number is said to be in the same group .
Group permissions apply to everyone else with the same group number .
For example, the file phone.numbers may have permissions set as rwxrwxr- . This would mean that the owner of the file can read the file, write to it, and execute it.