Mesh is when two computers connect via a Scratch project. I'm not very good at it, but Jonathanpb had a nice guide to it. I'll get you the link
EDIT: Here it is http://scratch.mit.edu/forums/viewtopic.php?id=32046
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Mesh is a feature of Scratch that the Scratch team didn't implement into any version of it. It allows two computers to use the same project, so you can basically make two player games. It's buried in the code for Scratch, you just have to know how to get it out and use it.
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