Turbidity

Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye.  The units of turbidity are known as Jackson Turbidity Units (JTU) or Nephelometric Turbidity Units (NTU) are a key test of water quality.  A practical example of turbidity would be muddy water.  The more mud present in the water, the less transparent and more turbid the water becomes.