A backup node is a secondary node in a blockchain network that helps maintain and ensure the security and reliability of the network. Unlike primary nodes that actively participate in validating transactions and blocks, backup nodes provide support in case the main nodes experience issues.

These nodes store a complete or partial copy of the blockchain, allowing them to quickly take over if a primary node fails. This redundancy is crucial for preserving the integrity of the network and preventing data loss. By having multiple nodes backup the network, it becomes more resilient to attacks or technical failures.

Users may set up backup nodes for personal reasons, such as enhancing the stability of a particular blockchain they use or engage with. Having multiple nodes also improves overall network performance, as it distributes the workload and reduces the chances of congestion. This way, backup nodes play a vital role in contributing to the robustness and sustainability of the blockchain ecosystem.