What is a 'String boundary' in an http request?

[jinduy]

im lookin at sample code and i see that this particular author takes into account something called a 'string boundary' which sends a bunch of hyphens over to the server i think.

http://forum.java.sun.com/thread.jspa?forumID=31&threadID=451245

anyhow... what exactly is a string boundary for? (ie he has a method createBoundary())

thanks in advance