Actions make it easy to repeat redundant tasks, such as changing photos to black and white, or resizing many images to a smaller size.
Part of Photoshop CS5
Part Type Interface
Screenshot Actions panel.jpg


Actions are a quick way to repeat redundant and repetitive tasks, such as resizing many images from a site visit or making a folder of images all black and white. More complex results can also be achieved if a specific end product is desired.

Actions basically allow you to record the buttons you hit as "steps", which you can then use to effect other images without having to repeat the clicks. They can be as complex or as simple as you want. Start by making a new action, naming it and then hitting record. Everything you do will be recorded until you hit the stop button in the actions toolbar. Don't forget to complete the entire action, which may include not only the "effect", but also saving the image to a specific folder and then closing the image. If you do not record these steps in your action, you'll be left with a large amount of files open and edited to your liking, but none are saved or closed.

A workflow that goes through the creation and use of Actions can be found here:
Using Actions for Repetitive Tasks in Photoshop