RSS is a way to stay updated with a live feed of content. You use an RSS reader to subscribe to content that is updated automatically for you. This content can also send you an alert when an update is out.
This is a great way for following content on a website. For example, you may want to follow an actor you admire and want to know what musicals they may be in so you can order tickets. RSS also saves you time and ensures your privacy is secure.