A price feed is the stream of prices that a tokenized asset, a checkout, or a settlement policy listens to. For a tokenized stock it is the program's own source for the underlying's price; for a checkout it is the FX or market table that converts an invoice currency into the asset being paid.
Feeds fail in two directions: stale (the price was right an hour ago) and thin (the price comes from a pool too small to absorb size). Robust systems name their feed per asset kind - market feeds for market assets, FX tables for pegs - instead of pretending one source fits both.
U.CASH prices each asset from the feed appropriate to its kind: on-chain markets for crypto, issuer feeds for tokenized equities, and fiat FX tables for stablecoin pricing. Asset and rail pages state which is in use.
Every term behind the rails, the assets, and the settlement.