Several people ask: "What is the hashtag aka # symbol in Twitter?" And I answer: "It is a way to organize a conversation on Twitter. Anyone can start one." And sometimes that doesn't get understood by the person seeking the answer to this question. So I did a little Googling to find out who started the #followfriday hash tag, which is one of the most well known uses of the # (hashtag). #followfriday is now a tradition on Twitter on Fridays, where people name a few Twitterers who they enjoy following. It is a way to recommend people to help them gain new followers. So perhaps this will help clarify the hashtag question and how it is used:
One day, this guy named Micah Baldwin was reflecting on his wonderful friends, who he followed on Twitter, and thought to himself: "I want others to follow them too."
(Quick note from Katie: There is actually an Arabic word for this...it is when you like something so much that you want someone else to enjoy it...like you are eating a piece of blueberry pie with ice cream on top, and you are down to your last bite, and your friend comes in, and you insist that your friend takes the last bite so that she too can experience it.)
So Micah logged into his Twitter account and said to no one in particular (aka all of his followers): "I am starting Follow Fridays. Every Friday, suggest a person to follow, and everyone follow him/her. Today it is @fancyjeffrey & @w1redone (who is now @dannynewman)."
Micah then sent a few Twitter messages (aka "tweets") to some key people, who may or may not have helped spread it (they thought it was spam), and went to a meeting. When he came back, he logged into Twitter again and used some tools that measure certain activities on twitter, and discovered that #followfridays had taken off! It was in use by people on Twitter from every corner. Pretty soon, people were just using it, and did not even associate it with Micah anymore, they were just spreading Twitter love for people who they liked to follow.
Because of the interest, Micah has now created a website called Follow Fridays.
This is one example of one hashtag, made useful by the people, for the people. So, you could make up a hash tag right now if you wanted. If it's catchy and fun to use, it just may become an "official" Twitter term!