A block chain, or blockchain, is a distributed database that maintains a continuously-growing list of data records hardened against tampering and revision (see Git repository design).
W3C Blockchain Community Group
Discussion of blockchains for the Blockchain Community Group and workshops
Blockchain Cryptography for Developers: ECC, secp256k1, SCrypt, AES, Wallets
How blockchain could change Web-based content distribution
http://www.bitcoin.ninja/ - Bitcoin Ninja