What is Infiltrator?

Infiltrator definition and meaning on Dictionary terms:
verb (used with object), inA.filA.tratA.ed,
to filter into or through; permeate.
to cause to pass in by filtering.

to move into (an organization, country, territory, or the like) surreptitiously and gradually, especially with hostile intent: The troops infiltrated the enemy lines.
to pass a small number of (soldiers, spies, or the like) into a territory or organization clandestinely and with hostile or subversive intent: The intelligence agency infiltrated three spies into the neighboring country.

verb (used without object), inA.filA.tratA.ed,
to pass into or through a substance, place, etc., by or as by filtering.
Pathology. to penetrate tissue spaces or cells.

something that infiltrates.
Pathology. any substance penetrating tissues or cells and forming a morbid accumulation.