Whenever you are on Twitter, you will see people tweet with code like #ipod or #iphone or something like that. These are called hashtags; Hashtags # are used to identify a topic on Twitter,
In the world of Twitter, hashtags — # — are used to create discussions about some particular topic, which helps people to track a conversation.
Add symbol (“#”) to the front of a word to make it a topic. For instance, #ipod is where you can find lots of iPod tweets. Hashtags can occur anywhere in the tweet, there are no formal rules for hashtag usage.
To search a topic go to http://search.twitter.com enter the hashtag or keywords in the search box and result will bring up what everyone is saying about iPod.