Twitter is a free social network that enables its users to post text based messages limited to no more than 140 characters that are referred to as "Tweets". Twitter was created in 2006 and gained prominence in the public consciousness in 2008 and continued mainstreaming in 2009 through celebrity adoption and usage. Twitter is often also called a "micro-blogging" service, although its evolution into a conversational tool gives it more of a sense of a very large chatroom.
Tweets are posted on the author's profile page and are delivered to their subscribers, which are also often referred to as "Followers", in the form of a Tweet Stream. Subscription to a user is an entirely opt-in process on the part of the subscriber.
Twitter allows its users to send their Tweets through its website, cellular Short Message Service (SMS), or through applications developed by third party developers using the Twitter Application Programming Interface (API). This functionality allows users to engage the service from not just their desktop, but generally anywhere there is a cell phone signal. Use of Twitter through SMS does not require the user to have a "smart phone" that is able to connect to the internet. Although Twitter is a free service, there may be additional phone usage fees from your cell phone carrier if SMS is utilized with the service.
Twitter Resources
PIO Social Media Training On Twitter
This is our Twitter account
The Official Twitter Blog
Official word on developements from the team at Twitter
Twitter System Status
Updates on the status of the Twitter service
Twitter's Facebook Fan Page
The Twitter service's Facebook Fan Page