It's not a particularly common phrase. I guess that it means that the data has been 'pre-packaged' - i.e. that it has been pre- or -post- processed into a form that makes it simpler for later processing. It could also possibly mean that the data has been 'fabricated' for testing purposes. Rather than allowing users to put random data into the system, a set of test data has been pre-prepared ready to feed into a system to test it out. You would have to use context to work out which of those it could be.