I found Eris's definition of blockchain and explanations of the difference between private/permissioned and public/unpermissioned blockchains to be one of the out there.
Recommend reading their detailed primer on permissioned blockchains after.
Bitcoiners having trouble wrapping their heads around how a blockchain without a valuable token could be of any interest should take a look.
The TL;DR is that the blockchain that Bitcoin provides is revolutionary and allows us to do a whole bunch of things that were impossible with previous technology.
Private or permissioned blockchains allow us to do many things that, while possible with previous technology were rarely done because they weren't easy or elegant. Private blockchains are evolution; the Bitcoin blockchain is the revolution.Read more...