Turbidity

Turbidity is a measure of the clarity (or murkiness) of water caused by suspended or colloidal particles. Highly turbid waters are those with a large number of suspended particles which interfere with the passage of light through the water. Turbidity in water is caused by particles of inorganic matter such as clay and silt, as well as organic matter, plankton and other microscopic organisms.

This is the common definition for Turbidity, other definitions can be discussed in the article