Quorum Certificate
In modern BFT consensus protocols (notably HotStuff), an aggregated Threshold Signature over 2f+1 votes for a particular block in a particular view. A QC is a constant-size proof that a quorum has voted, replacing the linear-size collection of individual votes used in earlier protocols like PBFT. Chains of QCs (parent-pointers) realise the three-chain commit structure of HotStuff and the safety arguments of its successors (Bullshark, Mysticeti).