Decontamination is the process of removing dangerous substances and organisms from objects and people.
In the 22nd century, NX-class starships featured a specialised facility for decontamination of personal returning to or visiting the ship. The decontamination chamber was a secured location adjacent to the launch bay where the ship's medical officer could dispense specialised decontamination gels to be applied to individuals in the chamber to cleanse them of contaminants. (ENT episode: "Broken Bow")
In the 23rd century individuals were required to undergo decontamination procedures after accessing power units on Constitution-class starships, even if they wore engineering suits for the procedure. (TOS comic: "UK comic strips, first story arc")