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1.
n. A social networking status update, Tweet, or post that contains an unnecessarily large number of tags or tagged names often unrelated to the context of the post.
lol, did you see that guy's uploaded photo? he tagged the whole school! that is an epic Mashtag right there
by Catfishdogg March 16, 2011
 
2.
Not to be confused with (#) "Hash Tag", the (+) Mash Tag was created by Oklahoma native Paige Stiner to be used in the place of Twitter's "Hash Tag" on Facebook in 2011. It can be used when you are specifically talking about one topic and you want to make it known, it can also be used to add comedy or emphasis to a comment made. While a Hash Tag makes things searchable on Twitter, the Mash Tag has no real function. It is said to be a trend started to convince Facebook users to stop using Hash Tags where they did not originate.
That was quite a win for Oklahoma!

+OKC

+ThunderUp

(+)-is the "Mash Tag"
by Modern Webster June 05, 2012