An extended action is an action which takes more than an instant to resolve. For example, a character may wish to search a library for specific occult lore, repair an engine, or break down a door.
The Storyteller, Revised Storyteller and Storytelling systems all contain rules for extended actions. These rules are generally only used when it is important to know how long a task takes to complete, as well as how well it is executed; time-consuming actions in which the character may take as long as she likes are resolved in the normal way.
Typically a player performing an extended action will repeatedly roll the appropriate dice pool until she achieves a set number of successes. The number of rolls indicate how long the character spent completing the task; the time scale is determined by the Storyteller or by specific task-related rules, and may be anything from a single turn per roll (typical in combat situations) to days or even weeks.
Extended actions are sometimes also contested actions.