Tethering means your phone use PC Internet use
Tethering is talked about when you connect a PC or laptop to a mobile phone or PDA to connect to the Internet in this way. This connection does not always have to happen physically with (USB) cables, but can also be done via infrared or Bluetooth. If the mobile phone has an internet connection, the laptop can use the Internet in this way. Not all mobile providers want to allow this, because on the phone often an unlimited data bundle is taken, and people will not purchase UMTS dongle in this way.