An advancement token is a token in Android: Netrunner that is used to indicate when a card has been "invested in" by the Corporation. The primary use for advancement tokens is to advance Agendas up to their advancement requirement so that they can be scored, but other types of cards can be advanced as well to give them additional effects or to be used as bluffs.
Although the Corporation has an action for advancing cards, advancement tokens can be added, removed, and moved to and from cards through various card effects as well.