What do BFT and PBFT (Byzantine Fault Tolerance / Practical BFT) mean?

Byzantine Fault Tolerance is a system's ability to reach agreement even when some participants are faulty or actively malicious; PBFT is a practical, efficient algorithm achieving it among known participants.

Permissioned blockchains typically use BFT-style consensus (like PBFT) among a small known writer set — lighter than Proof of Work, so faster, but tolerating far fewer untrusted writers.