Product feed
A product feed is a machine-readable file listing a catalogue: one entry per sellable item, carrying an identifier, a title, a price, an availability state and a link back to the product page, in a format built for a program rather than a reader.
A feed is how an agent gets an overview without fetching every page. It is also the cheapest thing to get right, because most platforms generate one already and the work is checking that it is complete and current rather than building it.
The failure mode is drift. A feed that was accurate at launch and has not been regenerated since describes a store that no longer exists, and an agent has no way to tell which of the two versions of your price is the real one.
Why it matters to a store
A stale feed is worse than a missing one. A missing feed makes an agent read your pages. A wrong feed makes it confidently recommend a price you will not honour.