Dental plaque is a biofilm of microorganisms (mostly bacteria, but also fungi) that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found between the teeth, on the front of teeth, behind teeth, on chewing surfaces, along the gumline, (supragingival) or below the gumline cervical margins (subgingival).


Source: https://en.wikipedia.org/wiki/Dental_plaque