A VDF, also known as a proof of time, is a sequential operation that takes a prescribed amount of time to compute (and which cannot be accelerated by parallelism) and which produces an accompanying proof whose result may be quickly verified. This must be done in a group, for which Chia uses ideal class groups. You can learn about them in our class group document. Timelords usually run three VDFs at a time for the three internal blockchains of the Chia blockchain. They run as vdf_client processes.
