The term 'Blockchain' is meaningless
There seems to be no single clean definition of what “Blockchain” actually means. There are a lot of woolly statements, several of which are clearly either wrong or too narrowly focused. This article goes into some of the different definitions and why they are wrong and then the implications of this from a business but also a legal perspective.
I personally think the definition by Mike Gault, CEO of Guardtime, is the closest:
“Blockchain is an append-only data structure that contains data records that are cryptographically linked together. Data records are added to the data structure when multiple distributed parties come to consensus based on pre-agreed rules.”