Fluids providing cooling and lubrication in metal working operations (metal removal) and partially in forming operations of (in most cases) metal workpieces. There are many traditional denominations: cutting oil, soluble oil, grinding oil, fully synthetic oils, metal working fluids, etc. According to DIN 51502 and DIN 51385 coolants are divided into two main groups:

1. Non water miscible coolants: Are applied undiluted (grinding oil, deep drilling oil, machining oil, cutting oil, etc.)

2. Water miscible coolants (water mixed metal working fluids): Are applied diluted with water.
a) Emulsifiable coolants (in application: coolant emulsion): Contain water insoluble components (in most cases as base oil).
b) Water soluble coolants (in application: coolant solution): Contain only water soluble components.