Byzantine Fault Tolerance (BFT) is a consensus algorithm designed to achieve fault tolerance in distributed systems, particularly in blockchain networks. It's based on the Byzantine Generals' Problem, which solves the issue of reaching consensus in a system where some nodes may be faulty or malicious.

BFT ensures that:

1. _Consensus is reached_: Even if some nodes are faulty or malicious, the system reaches consensus on a single, trusted state.

2. _Faulty nodes are tolerated_: The system can continue to function even if some nodes fail or behave maliciously.

3. _Security is maintained_: BFT ensures the security of the system, preventing faulty or malicious nodes from compromising the network.

BFT algorithms are designed to:

1. _Detect faulty nodes_: Identify nodes that are not behaving correctly.

2. _Isolate faulty nodes_: Prevent faulty nodes from participating in the consensus process.

3. _Achieve consensus_: Reach consensus among non-faulty nodes.

Some popular BFT algorithms include:

1. _PBFT (Practical Byzantine Fault Tolerance)_

2. _SBFT (Simple Byzantine Fault Tolerance)_

3. _dBFT (Delegated Byzantine Fault Tolerance)_

BFT is used in various blockchain networks, including:

1. _Hyperledger Fabric_

2. _Corda_

3. _Quorum_

BFT offers high security and fault tolerance, making it suitable for enterprise blockchain applications and permissioned networks where node reliability is crucial.