Glossary
Verifiable Delay Function (VDF)
A function that takes a prescribed amount of sequential work to compute but produces a proof anyone can check quickly, guaranteeing real time has passed.
A VDF requires a fixed number of sequential steps to evaluate — the computation cannot be sped up by adding more processors. Once the output is produced, it comes with a short proof that anyone can verify almost instantly, so a slow-to-compute result becomes cheap to check.
This asymmetry makes VDFs useful for unbiasable randomness: a beacon can mix together inputs and then run a VDF, so no participant can grind on candidate values to bias the result. Ethereum researchers studied VDFs alongside RANDAO to harden leader election, and projects like Chia use them as a core part of consensus.