The terms page and spread are fairly interchangeable in Affinity. If you're working with single pages rather than facing pages, the terms are interchangeable. However, for facing pages, the term spread becomes more significant.
At document setup, you can create pages for your document. Pages can use a portrait or landscape orientation.
Pages can be presented individually or, by enabling the Facing pages option, arranged into spreads.
Using facing pages means you'll be working with left (verso) and right (recto) pages displayed at the same time, e.g. a gatefold center spread of a magazine.
Facing pages can be arranged vertically or horizontally.