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.
Apps are downloadable mobile phone and tablet applications that you can run directly from your handset or tablet.
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.)