A cover is essentially an envelope (it got it's name because it covers the contents), usually stamped and those stamps cancelled. Here's some examples of fancy

A cover is essentially an envelope (it got it's name because it covers the contents), usually stamped and those stamps cancelled. Here's some examples of fancy covers: https://store.usps.com/store/results/collector-s-zone-first-day-covers/_/N-1omg4l9 https://store.usps.com/store/results/collector-s-zone-first-...