1) Having an item in your possession that is ready to be sold and/or shipped out to a consumer.
2) A car that has no performance modifications on it. Most street racers who race with American muscle cars or high end European sports cars claim that their "stock" cars will beat any "moded" import from Japan. 99 times out of 100, they are right.
1) Yes, Mr. Smith, that item is in stock. OR Sorry, Mr. Smith, we're out of stock for that item.
Verb. To use a stock image as your profile picture on social media. The image could be related to one of your interests, your job, etc., or just be a funny picture.