Supply
Plain definition
Supply is the full relationship between a good's price and the quantity sellers are willing and able to offer, holding everything else constant. It is usually drawn as an upward-sloping curve: higher price, higher quantity supplied.
In economics
Supply describes producer behavior under costs. A change in the good's own price moves quantity along the curve, while changes in input costs, technology, taxes, subsidies, prices of related goods, expectations, or the number of sellers shift the whole curve. Together with demand, supply determines market price and output.
Example
If wheat prices rise, farmers plant more wheat — a movement along the supply curve. If a new harvester cuts harvesting costs in half, farmers supply more wheat at every price, shifting the entire curve right even though the price itself has not changed.
As with demand, people confuse supply with quantity supplied. A price change alone moves quantity supplied along the curve; only a non-price factor (costs, technology, policy) shifts supply itself. Supply increased should never mean more was sold because the price rose — that is just more quantity supplied.