> The blockchain is a merkle tree structure shared via p2p communication over a protocol designed to prevent double spending.

I'd say "The blockchain is a Merkle tree structure with a consensus algorithm which selects a canonical path to a leaf node at any given time."

I don't think preventing double spending is a meaningful concept for non-cryptocurrency blockchains, since those have nothing to spend. Whether we accept that such things are blockchains determines whether this distinction makes any sense. Though, if all blockchains are cryptocurrencies then there's not really any need to separate the two terms.

Yes you're right, that's a better generalised description of them. Of course that's what I meant by "double spending" (essentially, the list becoming a graph, ie forking), but precision in communication is important.