Glassbreak is a maximum-security prison for suprahumans, first mentioned in Not a Good Day to Be Empowered.
It is used to contain individuals who are deemed to pose an unacceptable danger to humanity and the planet. Inmates are kept frozen in cryogenic suspension, and all guards are vetted by a telepath before being hired. Mindfuck performed this duty until her untimely death.
Not a Good Day to Be Empowered implies that all current inmates of Glassbreak are supervillains, with Empowered being the first time the Executive Council voted to incarcerate a hero for the greater good. Several characters comment that sending a hero to Glassbreak could set a dangerous precedent. Ultimately, Emp is not imprisoned in Glassbreak, due to her being rescued by Manny and then finding proof that her knowledge of Object 524 no longer poses a danger.