A person who steals jokes and material from people on Twitter and tweets them as if they were their own, with no attribution, re-tweet, or credit given.
Can also be used as a verb, as in to "zachishere" someone's joke or material; see also, "zachishered".
Wow, that girl stole my joke without giving me credit or re-tweeting me! What a total zachishere!
You totally got zachishered by that guy!