Vaseline is a commercial name for a petroleum jelly product.
Products other than petroleum jelly are also marketed under the trade name Vaseline, but a reference to just Vaseline almost always means petroleum jelly. The name is sometimes used as a generic for any make of petroleum jelly.
It is a convenient lubricant, for example for use in masturbation and when inserting a dildo or a butt plug. However, being oil-based it can destroy the effectiveness of latex condoms and damage latex clothing.