1. A technically bankrupt company that is kept alive with large infusions of government money for the sake of "stability" in the U.S. financial system. 2. A large financial company with negative net worth that continues to operate, despite having no clear path to solvency. 3. The UnDead of Wall Street.

A company that is considered too important to allow to go bankrupt, and ends up sucking on the lifeblood of the United States (aka its money). Members of zombie companies are permitted to take bonuses of any size, thus contributing to the general blood sucking.