What is IR blaster?

As I read reviews of dvd recorders, different units are said to have or lack "IR Blaster". What does it do? I like to programmed (unattended) recording from off-air (antenna) TV, I don't foresee getting cable or dish in near future. So a typical situation might be:

record Ch 7 from 5pm-6pm every Tuesday,
Ch 11 from 9pm-10pm every Saturday, and
Ch 5 from 4pm-5pm only tomorrow.

Do I need to worry about if my machine will have IR blaster or not?

Finally, for a VCR replacement, I would like to use re-usable media and am confused by various types of DVD's. Is there any reason to choose DVD-RW, or DVD+RW, or DVD-RAM or they are all equally good?
As long as the device you are recording with has a TV tuner built in you won't need an IR blaster. An IR blaster will turn on your cable box, sat reciever etc and change it to the right channel for recording.
To expand on Rwwear, the blaster is an IR output from the dvd that will send commands to other pieces of equipment to control them. ie the dvd player can turn on your cable box and switch it to the correct channel when it is time to record. Some blasters just use IR repeaters while nicer ones actually can plug into the IR in in the back of another unit (this avoids any interference).