Stock:

• The total available quantity of goods with a producer which can be offered for sale in the market as per the ability and willingness of the seller is called stock.
• For example, a trader of oil in Rajkot has 500 packets of oil. This means the trader has 500 packets as stock if he is not able and willing to sell them in the market at a given price at a given point of time then supply is zero even with stock of 500. But, if he is able and willing to sell 300 packets from the available amount then the supply of oil is 300 packets.
• In other words, Stock = 500 packets of oil
  Supply = 300 packets at ₹ 100/packet.

Important concepts to understand meaning of stock:
(A) Willingness to sell:
The total quantity of a good available with a producer or trader is not called supply but is called stock. It will become supply only when he is able and willing to sell it at a given price at a particular point of time.

(B) Ability to sell:
Ability to sell depends upon the availability of stock. For example, if a trader of oil desires to sell 1,000 packets of oil while he has an available stock of only 500 packets then the ability to sell is only 500 packets. Thus, supply is 500 packets.