Supply means the amount of something available to use or buy. When a store has a good supply of notebooks before school starts, it has plenty in stock for customers. When your teacher checks the classroom's supply of pencils, she's seeing how many are left for students to use.

The word works as both a noun and a verb. As a noun, it refers to the quantity available: “We need to increase our supply of firewood before winter.” As a verb, it means to provide what's needed: “The cafeteria supplies lunch to students every day.”

In economics, supply pairs with demand to determine prices. If many farms supply tomatoes during harvest season, prices drop because tomatoes are plentiful. If a drought reduces the supply, prices rise because tomatoes become scarce.

You'll also hear supply in phrases like supply and demand, water supply (the water available to a town or city), or supply chain (the system that moves products from factories to stores). During emergencies, people stock up on supplies like food, water, and batteries.

The word suggests having enough of something on hand when you need it. Running out of supplies can mean trouble, whether you're on a camping trip or running a business.