Shorthand I associate with Dave Winer - short for Big Company (Big Corporation). Typically used with disdain, referring to bureaucracy, CYA behavior, etc. Could apply to a software maker (e.g. Sun) or a big customer (typically Enterprise buyer of SAP, overpriced CMS packages, etc.).
Often smells like it should just be called ObnoxiCo.
Brad De Long on "The Corporation as a Command Economy" - The corporation flourishes because it is useful to (and thus favored by) the government, because we have a set of institutions to govern corporations that greatly limit the power of the forces that destroyed the Soviet planned economy, because our technology requires increasingly fine coordination of different aspects of the production process, and because our corporations are embedded in a market economy that imposes a substantial amount of competitive pressure on corporations. Even small lapses relative to its competitors in a corporation's efficiency as a productive organization can destroy the corporation as a profit-making organization--and corporations that are not profit-making organizations do not survive.