What is a twitter hashtag? ?

[David]

[Nate]

It's a way to make a topic trend. For example, #myspeedoistoosmall

[♥London♥]

Its a way to trend a topic, depending on how many people tweet something like this;
#LikeABoss
It will show up in 'trending' topics on the right hand side on the twitter homepage if LOADS of people tweet it.

[Dest]

It's a way to make a topic trend, it's also a good way to keep other people who follow that hashtag, about updates.