Basically, a blockchain is a permanent inmutable record to exchange data, money, goods, and services. Its independently operated by Internet users and its distributed amont their computer network.
A BC is a transactional database distributed among all participants, without the need to trust each other through a central administrator. Can be accesed but not edited by all. Its the book of the truth.
BCs constrast with traditional databases: SQL, NoSQL because these are controlled by a single entity, even when having some distributed architecture.
The BC of Bitcoin makes impossible the double spending issue, maintains a permanent control of the transactions, and this makes a central bank useless.
Blockchains work like a ledgers but not all ledgers are blockchains. Criptocoins and digital coins are not the same either. A cryptocurrency is a pseudo-coin like BTC. A digital coin could be eur, usd, etc. or a private share ledger.
Criptocoins are not just a kids game: they are supported by a powerful cryptography and circulate through a network that does not know about frontiers.