In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is more commonly known as thermal imaging.
My Canon 5D DSLR has had the infrared blocker in front of the sensor removed and replaced with a filter that removes visible light. This filter is behind the mirror, so the camera can be used normally – normal shutter speeds, normal composition through the viewfinder, and focus – all work just like a normal camera.
When the photos are shot they look “red and dreamy”, then I convert them to black and white on the computer, where they take on a life all their own.
Vegetation being green takes on reflective qualities much like snow. The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze, compared to visible light. Bright blue skies become black, clouds take on different shapes.
Much more information on Infrared Photography can be found here.