Concept

A type of node (blockchain node)- specifically, a bitcoin node- that stores only a part of the blockchain, and hence the amount of data it stores is limited to a subset of the blockchain. Since pruned nodes require smaller amounts of data storage to maintain its consensus, more users can have more room to participant given a user’s lower tech capabilities. A pruned and full node differ in the amount of blockchain data each can store. A full node stores the entire network, including every transaction that was conducted on the network. In contrast, a pruned node only stores a sector of the blockchain, accommodating certain users’ limited resources (e.g., limited storage capacity). Pruned nodes may also allow users avoid the longer wait time for downloading the entire records.

Importance

Pruned nodes represent a line of support necessary to the stability of the network. Full nodes come at the core, while pruned nodes provide additional support and help keep track of the integrity of the entire network. The more nodes are in a network, the better its security is. Given its limited scope, a pruned node does fully verify all transactions, but it just doesn’t record or produce all the historical data after completion of verification. A full node is said to be pruned or un-pruned (archival node). Users can move from un-pruned nodes to pruned  nodes, but not the other way around (otherwise, the entire network has to be downloaded and re-verified).

A pruned node extensively reduces the amount of storage space (hard drive space) required to validate entered, new transactions. Pruning helps users avoid the long time needed to download and store previously verified and recorded transactions. For example, a pruned node operator can define how long on the network it would go, considering any transactions that have been validated for a certain number of successive blocks as immutable. The pruned node operator would compress all data prior to the defined number of blocks that have been verified into a single, cryptographic hash.

Synonyms

Pruned nodes are a type of full nodes in the sense that they can function as such but for a part of the network. Therefore, at times these nodes are known as full nodes (though practically, full nodes and unpruned nodes are used interchangeably to denote the same meaning (in term of scope of coverage).