IR is infrared I am talking Radio frequency
The ability to allow the cable signal to flow through the settop box.
IE when off you can use the digital tuner on tv to view some of the channels.
Normally Tv's, VCR's (back when they were popular) used a specific channel
(I think it changed a few times as to channel #) that must have had a time date code
included that was used to set clocks.
I remember my older boxes had a setting where I could enable or disable RF Bypass.