Block chain is the name for a technology that is commonly used to keep track of assets in a computer program, mostly when it refers to Crypto-currencies, or digital money. The idea of keeping a public ledger in a network of computers to secure the data is much older, but has recently bloomed into the common awareness because crypto promises to be a problem solver for what much of the population still see as obvious problems of this society.
Currencies like Bitcoin, Ether and many others are booming, as people rush to make their fortune in it. Still, the developments are quite new, and in full flux. With the big player like IBM, Microsoft and others involved in it, it does promise to be a technology that will graetly change over the next few years.