What it Is
A DVR (digital video recorder) allows the user to digitally record, save and pause television programs. The information is saved to an internal hard drive and can be saved for however long the user sees fit and deleted with the press of a button. Everything is done from the DVR, so there's no need to buy blank VHS tapes or writable DVDs in order to be able to watch something you won't be home for, or to watch something again.
How it Works
A DVR hooks up to your television in much the same way a DVD player or video game console would. Once you hook the coaxial cable that provides your cable television signal into the DVR, it then directly processes all television signals it receives through its built-in TV tuner. It automatically records what you're watching (though it doesn't permanently save it to the hard drive unless you tell it to), which is how you can pause and rewind even live events.
Some DVRs come with two built-in TV tuners. So in addition to recording what you're watching, you can record something on another channel simultaneously. This is extremely helpful if two programs are on at the same time and you don't know which to watch. Models with two tuners also allow the user to hook up two TVs to the same DVR at the same time. Each TV would be able to give it specific commands, and both TVs could access the programs stored on the hard drive whenever necessary.