Facebook is a social networking website where you create a profile that tells others about you through photos, videos, links to web content, lists of your interests, and updates about what you're doing.
Twitter is a social networking site that updates your community about only one aspect of your life: What you're doing. Your Twitter account is similar to a blog, but posts are limited to just 140 characters. Each post is called a "tweet."
RSS, most commonly translated as "Really Simple Syndication", is a family of web feed formats used to publish frequently updated works such as blog entries, news headlines, audio, and video in a standardized format.
Flickr is an image and video hosting website and online community platform. In addition to being a popular website for users to share personal photographs, the service is widely used by bloggers as a photo repository.