Twitter: The name was coined by Noah Glass, the co-founder of podcasting company Odeo and an early driving force behind making Jack Dorsey's idea for Twitter a reality. Glass flicked through the pages of a dictionary until he stumbled upon twitter, meaning 'the light chirping sound made by certain birds', 'light, tremulous speech or laughter' and 'agitation or excitement; flutter'.
It's true that @Noah never got enough credit for his early role at Twitter. Also, he came up with the name, which was brilliant.— Ev (@ev) April 13, 2011
Subsequent words born out of Twitter, include the noun 'Tweet' (a message of up to 280 characters posted on Twitter), the verb 'to Tweet' (the act of sending a Tweet) and 'hashtag' (a word or phrase preceded by the # symbol that can be used as a link to see Tweets about the same topic).
Sources: Hatching Twitter by Nick Bilton | Tweet by Evan Williams | Twitter glossary