What does the permission 755 on a directory mean?

Permissions 755 on directories mean the following:

• The octal value 755 corresponds to the permissions rwxr-xr-x.
• The owner of the directory has read (r), write (w), and execute (x) permissions.
• The group and other users have read (r) and execute (x) permissions, but not write.

For directories, the "execute" (x) permission means the ability to enter the directory and search for files.

Thus, with permissions 755, the owner can modify the contents of the directory, while others can only view and enter it, but cannot create or delete files.