[lawrenceyan]

Do you mean Proof of History? The concept is made concrete in Solana, but actually any blockchain that hashes a set of transactions in each of its successive slots/blocks can be used to prove that time has passed.

You can verifiably be assured of a temporal ordering between transactions that were hashed in different slots because the output of a slot/block is hashed and used as an input for the next block/slot.

[jhugo]

Solana claims to prove that a certain duration of time has passed, which is a different and much stronger claim than just temporal ordering. The details of their claims, last I heard (which was some talks in Berlin years ago) were extremely hand-wavy and apparently not well understood even by some people working on the project.