Lubrication
Lubricant is a term used for a substance which, by removing friction, makes it easier to slide one thing against another. This has many implications; one example would be using a substance like vitamin oil on stretched lobes to make the insertion of jewelry into a piercing easier and more comfortable.
Lubrication is also used between needles and skin during tattooing and piercing.
Another example would be the use of a water-based lubricant on a sexual barrier such as a condom to make penetration easier during sexual activity. Both the male and female body produce their own lubricating substances, semen for males and vaginal discharge for females.
Some oil-based lubricants react badly with latex, breaking it down so that it tears. Oil-based lubricants should never be used with rubber gloves or condoms!