Extended Action
Extended Actions require you to spend an extended length of time performing some task before the action completes. Using an Extended Action requires concentration and attentiveness, but it is not subject to interruption the way that Cast Actions and Focus Actions are. If your Concentration is interrupted while using an Extended Action, you do not lose progress towards the completion of the action and instead simply pause the action until you can resume concentrating. This action type does not frequently come into play during combat.
Example
Fred the Blacksmith is Crafting a Sword [Extended Action, 1 day]. He is interrupted by a thief, stealing from his shop. After a merry chase down the streets, Fred apprehends the thief and hands him over to the town guard. He then returns to his shop to resume work on his sword. He's lost some time, but working just a little later into the night will make up for it.