Noise & noise reduction.

I have been reading 'The Digital SLR Handbook' by Michael Freeman. Throughout the book the term noise and noise reduction is used frequently. I am unfamiliar with these terms.

After some research I discovered that using High ISO and long exposures can increase ‘noise’. Noise can turn up as speckles and grain in your photographs. There are three types of noise.

Fixed Pattern Noise - Generally appears in very long exposures and is heightened by high temperatures.

Random Noise - Influences by the ISO speed and appears due to colour fluctuations above and below the image.

Banding Noise - Visible when reading data from the sensor, high ISO and in shadows.

Random noise being the most difficult to get rid of and fixed pattern being the easiest.