Block Chain
From wikipedia, a blockchain is a growing list of records, called blocks, that are linked together using cryptography. It makes use of hash value to get the integrity and avoid being tempered by illegal user.
Tutorials
Naivechain gives a simple intuition of the concept of blockchain. It removes the concepts or code of infrastructure of some specific application (e.g. Bitcoin or Ethereum). Thus it is a good place to begin the tour.
Additional links: