Barbell style piercing jewelry is composed of a straight bar and with a bead on each end, one or both beads unscrewable for removal and/or changing of the beads. Often one of the beads is fixed, either via epoxy or welding, so that only one bead is used to install or remove the jewelry.
There are also variations of the barbell piercing. Most common are curved barbells (mostly used for navel piercings), circular barbells and surface bars which are used in surface piercings.
This tag implicates piercing (learn more).