What's this called?

From: joto (a_at_a.com)
Date: 10/28/04 

Date: Thu, 28 Oct 2004 19:13:31 -0400

Hi, I need to turn off a certain electronic device X hours (3-4) after i
start it. I want this to happen automatically, so I need something that
goes between the device and the power outlet, which will automatically
switch off the juice after X hours, as if the device was unplugged. I
want it to be as easy to use as possible, so that there's just some dial
or some buttons where I can set the time after which the device is to be
turned off. It's running off of north american standard 120 V, 60 Hz, and
if the device is turned off reliably there could be a sfatey hazard.

What kind of thing would do the job/what's it called?

Thanks.