A stock trader or equity trader or share trader is a person or company involved in trading equity securities. Stock traders may be an agent, hedger, arbitrageur, speculator, stockbroker. Such equity trading in large publicly traded companies may be through a stock exchange. Stock shares in smaller public companies may be bought and sold in over-the-counter (OTC) markets. Stock traders can trade on their own account, called proprietary trading, or through an agent authorized to buy and sell on the owner’s behalf. Trading through an agent is usually through a stockbroker. Agents are paid a commission for performing the trade. Major stock exchanges have market makers who help limit price variation (volatility) by buying and selling a particular company's shares on their own behalf and also on behalf of other clients.