In cryptography and computer science, a hash tree or Merkle tree is a tree in which every non-leaf node is labelled with the hash of the labels of its children nodes. Hash trees are useful because they allow efficient and secure verification of the contents of large data structures. Hash trees are a generalization of hash lists and Hash Chains.
Both git repositories and bitcoin are specialized Merkle trees. Merkle trees are incredibly useful and general; they are used in many kinds of verification, especially of large chunks of data.
The terminology used in #bitcoin-wizards is to call it a merkelized dag, or merkle-dag. Similarly, we also refer to "Merkelized Abstract Syntax Trees", a way of hashing code originally proposed by Pieter Wuille and Russel O'connor that will probably be added to Bitcoin's scripting system eventually. Pretty much any data structure can have hash functions added to it to "merkelize" it, producing an authenticated data structure - [Peter Todd