Concept
Blockchain
A chain of blocks of transactions, each block committing to the one before it.
In practice
A blockchain is a replicated log. Changing an old entry means rebuilding every later commitment, in public, against everyone else who has the log.
It does not, by itself, create legal title, identify a person, or make a price.
What this page does not do
It does not price an asset, rank a protocol, or tell you to buy, sell, or stake anything.