People sometimes give me phone number like (XXX) XXX XXXX ext. XXX. I was wondering what does this 'ext. XXX' mean?
ext. is short for extension which is an internal number used within a PBX systems.
It is usually an additional short number and may or may not be related to the originally dialled number.
The extension number is usually requested and dialled once the caller is inside the local PBX system.
Users within the PBX can call each other by using only the extension number.