Any device that connects to the interface of a blockchain is called a node. Since anyone can open a node, even with their home computer, they can be located anywhere in the world.
Each node contains a complete record of all transactions that have been recorded on that blockchain, i.e. an up-to-date copy of the ledger. Nodes in a network can have different tasks depending on the structure of the specific blockchain. For example, they can be validators, miners or just store the blockchain history.