What is the difference between a 'shroud' and a 'stay'?
Short answer
Shrouds support the mast from the sides; stays support it fore and aft
Shrouds are the wire cables that support the mast laterally (from the sides of the hull). Stays support the mast fore and aft — the forestay runs from the masthead to the bow, and the backstay runs from the masthead to the stern. Both are standing rigging.
Quick check
What is the difference between a 'shroud' and a 'stay'?