What is Cabinet Impulse Response Loader?

I was doing some research on how to get hum out of my Satriani type distortion guitar tone (from Line 6 POD HD500, with Tascam US-2X2 USB Soundcard, Left Channel) that I recorded without rerecording (because sometimes I feel it won't be the same if I rerecord it, the freedom will not be there).
(In Google) Came across this term "Cabinet Impulse Response Loader", I know I can work with EQ in Sonar to get the hum down, but got curious about this "Cabinet Impulse Response Loader"... any plain explanation would be great for me to decide how I can take advantage of this in the future. Example:
http://lepouplugins.blogspot.com/2010/12/lecab2-vst-for-windows.html
What do you guys use most effectively when you come across with hum noise for distortion guitar? It becomes more obvious when you have to do a clip gain during lead part.
Thanks in advance..

Yeah, the 'Cabinet Impulse Response Loader' is just a plugin that takes a signal and makes it sound like it's been played through a physical speaker cabinet, and recorded by a microphone. Usually you need this after an amp sim to make it sound like a 'real' electric guitar performance. However, your Pod HD500 has this built in (unless you have chosen to bypass it).
 
If the hum was being introduced by the Pod then going straight into the PC and simulating the amp and cab there would help in future - but really, the Pod is professional kit and it should be possible to record that without problems if your setup is correct.