Unix file permissions: rwxrwxrwx
If you mean 4th, 5th & 6th char in above permission string, then it means the permissions(read, write, execute) applicable for the group on the file. This group name is displayed in the output of the command, 'ls -l', 4th column.

-rwxrwxrwx
Here 2nd position i.e. w denotes write. The person has permission to edit file.
If you are talking about 2nd group i.e 2nd rwx then it stands for group. It includes those users who are part of the group to which file owner belongs