What is a telescreen?

A telescreen, similar to a television in appearance, is a device installed in every home that consistently shows programming designated by the Party. The device runs day and night and cannot be turned off.

The voice came from an oblong metal plaque like a dulled mirror which formed part of the surface of the right-hand wall. Winston turned a switch and the voice sank somewhat, though the words were still distinguishable. The instrument (the telescreen, it was called) could be dimmed, but there was no way of shutting it off completely.

How is a telescreen different from a television