A stock or share of a company, commonly referred to as its "equity," is a fundamental financial instrument embodying the concept of corporate ownership. It serves as a physical representation of a person's or entity's ownership of a particular company, granting them certain rights and obligations that result from their ownership of the company.

The primary purpose of a stock or share is to grant its holder a reasonable claim to the assets and profits of the company. When an individual acquires shares in a company, they acquire a portion of its ownership. This ownership is reflected in a variety of privileges, such as access to the company's earnings, the right to vote on corporate governance matters, and even the potential to influence strategic decisions.

The idea of ownership through stocks is based on the principle of risk-reward. When a company is successful and profitable, its stockholders benefit from their ownership interest, as they are able to participate in the dividend distribution, which is a proportion of the company's profits distributed to shareholders. Furthermore, the value of the shares can increase if the company continues to grow and expand, thus increasing the total value of the investment. On the other hand, the value of a stock can decrease due to a variety of factors, such as market conditions, poor performance of the company, or economic uncertainty. This inherent risk highlights the fact that the value of an investment can change over time.