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I agree with tcarb. The meaning is in the attached content suggested in the tweet; the link, the tag, the @thatperson message.
The creativity becomes itself a link, to the next tweet, the next discussion, the next subject. Following, followers, groups, connections. So that the flow into and out of each tweet becomes the flow of creativity. But yes, one spike of 140 characters is too limited, in and of itself, to be an individual work.

Bob got it right. A Tweet is a digital Haiku. I am a fiction writer and use technology as a dimension in the story. I spent 20 years in the tech world. Have written some pieces on writing in the digital age. A Tweet is a "meaningful construct" for its readers - it need not be meaningful in itself but can point to something on the web that is meaningful for the sender or the recipient or both. This becomes tagging on the web. These types of cyber references are in the mind of the questioner when s/he asks the question - there is a way in which a tweet can convey a meaningful story for its reader.