In 1979, Ralph Merkle patented the concept of hash trees. It is a data structure that allows efficient mapping of large chunks of data in the form of a connected tree / linked list.
Consider it to be like an organization structure for data points. In such a linked set of hashed data structure, any small changes made to the data can be easily identified or spotted.
Cryptos are the best example of the use of Merkle trees.
The best resources for understanding Merkle trees can be found here: