Blogs are web sites on which individuals or groups of users record opinions, commentary, descriptions of events, or other material such as graphics or video on a regular basis.
Twitter is a social networking and microblogging service that enables its users to send and read messages known as Tweets.
Facebook is a social networking website that allows users to create profiles, upload photos and video, add other users as friends and exchange messages.
YouTube is a video-sharing website on which users can upload, view and share videos.
Flickr is an image and video hosting website and online community.
RSS (Really Simple Syndication) is a web feed format used to publish frequently updated content - such as blog entries, news headlines, audio and video.
A podcast is a program (usually audio, sometimes video) which is made available as a downloadable digital file.
(Some descriptions sourced from Wikipedia.)