From WoWWiki

A part of the game world that a Player character can loot by gathering or harvesting for raw ingredient items usable by professions or items required by quests.

Examples of resources:

• Herb plants (gathered with Herbalism).
• Mineral veins or deposits (gathered with Mining).
• Skinnable corpses (gathered with Skinning).
• Fish-able bodies of water (gathered with Fishing).
• Quest based nodes (Gaea Seeds, Shellfish Traps, Incendia Agave Plants, etc.)