Changes to a cryptocurrency network's protocol that are backward compatible are known as soft forks. This allows nodes who don't update their software to reflect the new changes to continue communicating with the network, even if they don't incorporate the new features or rules into the network.

A soft fork is a type of upgrade or modification to a blockchain protocol that is backward-compatible with earlier versions. Unlike a hard fork, which creates a permanent divergence in the blockchain, a soft fork allows nodes running the old software to continue participating in the network without disruption. This upgrade typically involves tightening or modifying the consensus rules, making them more restrictive.

During a soft fork, nodes that have upgraded to the new protocol will still recognize blocks created by nodes running the old software, ensuring a smooth transition. However, nodes running the old software will not accept blocks created by nodes using the updated protocol if those blocks violate the new rules.

Soft forks are considered a less disruptive method of implementing changes in a blockchain network, as they maintain compatibility with the existing network and require a broad consensus among participants to be successful.