Actually we can only see a very small part of the entire range of radiation called the electromagnetic spectrum . The electromagnetic spectrum includes gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves. The only difference between these different types of radiation is their wavelength or frequency. In addition to visible light, radio, some infrared and a very small amount of ultraviolet radiation also reaches the Earth's surface from space. Fortunately for us, our atmosphere blocks out the rest, much of which is very hazardous if not deadly for life on Earth.
Infrared radiation lies between the visible and microwave portions of the electromagnetic spectrum.
Thus infrared waves have wavelengths longer than visible and shorter than microwaves and have frequencies which are lower than visible and higher than microwaves. Near infrared refers to the part of the infrared spectrum that is closest to visible light and far infrared refers to the part that is closer to the microwave region. The primary source of infrared radiation is heat or thermal radiation. Even objects that we think of as being very cold, such as an ice cube, emit infrared. When an object is not quite hot enough to radiate visible light, it will emit most of its energy in the infrared.