Often used as a synonymous for dirt or polution.
In a precise definition contamination designates the presence of an extrinsic material on a surface or within a substance which has hazardous effects either regarding health or enviroment or function of a material or a process, depending on the context.
A field of particular importance is the contamination of surfaces with with biological substance causing infections.
Plasma cleaning is a most effective and secure process to remove biological substance even in minor content even from complex structured surfaces. Many sterilizing methods are able to kill biological substance but do not completely remove the remains. However regarding several health effects even these remains are active.