OK. Have you ever done the same thing twice in Photoshop? Let's say you wanted to scan and create a PDF from the crossword every day (I don't know, maybe you have a fetish or something). To scan it, you would follow the same steps every day in the same order without fail. Soon, you might think to yourself, "Hey, this here computer should be able to automate this set of tasks for me somehow."
Well, Photoshop DOES allow you to do just that with Actions. If you use Photoshop for any production-oriented task, you are missing a big boat if you aren't using them. And you are being a dummy. There. I said it.
Definition of an Action
An Action is a recording of a series of Commands in Photoshop to which you apply a name. Later on, you can play that recording back on a different file and have Photoshop do your work for you. They are mostly used to
Capture repetitive tasks that are to be applied to a series of files.
Walk a person through a technique in a step-by-step fashion.
However, these only hint at the power of Actions. Stick with me, and I'll show you how you can
Apply an Action to a folder full of files while you are off gossiping at the coffee machine.
Swap them with friends. Sad, nerdy friends.
Create a gargantu-Action by quickly combining existing Actions.
Apply a keystroke to your Actions.