Barrel means: A round (cylindrical) vessel, such as a cask, of greater length than breadth, and bulging in the middle, made of staves bound with hoops, and having flat ends (heads).. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.