More and more teachers are using Twitter to create a personal learning network as part of their professional development. A hashtag, or #, is used to transmit tweets to groups. To see more hashtags and learn how to use Twitter, start with this site: http://www.cybraryman.com/edhashtags.html
Here are some educational chat hashtags to get you started.
#edtech
#ellchat
#engchat
#iPadChat
#k12media
#mathchat
#scichat
#spedchat
#web20chat
#edchat
#artsed
#aspergers
#gtchat
#math
#science
#STEM
#lessonplans