An oracle is the pipe between the chain and the world outside it: a price feed, a sports score, a weather reading, signed and delivered on-chain so contracts can act on it. Every tokenized asset that tracks something is really tracking an oracle's word about that thing.
The engineering question is always trust distribution: one publisher is a single point of failure, so serious feeds aggregate many nodes, many sources, with deviations flagged. For payments, the feed's refresh cadence sets how stale a quoted price can be.
Tokenized assets on U.CASH price from the feed appropriate to their kind, issuer feeds for equities, Chainlink total-return feeds on Base, pool prices on Solana, FX tables for pegs, and each page says which.
Every term behind the rails, the assets, and the settlement.