"Twittering" is a word mistakenly used to describe the action of posting a comment on Twitter. It is primarily said by people who have never used Twitter before, and only heard about it from and friend or a T.V show.
The proper word would be "tweeting" (see tweeting)
Hey man, did twitter that message to your friends? - Guy 1
No, but I tweeted the post to my followers... - Guy 2
I think I'm going to be twittering this link to everyone I know! - Guy 1
It's called tweeting... - Guy 2
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