The Synopses are the (almost) human readable documents which constantly kept up to date, (unlike other historic docs like apocalypses and exegeses.) mostly after discussions at the p6l mailing list.
The Perl 6 design process began with a call for RFC (requests for comments) in July 2000 at The Perl Conference 4 (todays OSCON). In the next one and half year 361 RFC came in and Larry Wall sorted them and answered with the Apocalyses. Damian Conway tried to make them easier accessible and enriched them with examples. He got help from Allison Randal and so the Exegeses were born. But people today are not very patient and want a quick diff between Perl 5 and 6. That is why the Synopses were written.
comes from the latin word for compare. Its mostly used today by theologians (like apocalypse and exegesis too) who call the 3 gospels (except John's) synoptical gospels, because the tell almost the same story in the same order, even some parts are in each version different or missing.