To complete a sentence about financial securities.

The question asks to complete a sentence about financial securities.

• A financial security that represents an ownership interest in a corporation is known as corporate stock. A bond, on the other hand, represents a debt.
• Corporate stock, representing ownership, is considered an equity security. A debt security represents a loan.

Therefore, the completed sentence should be: "The type of financial security that represents an ownership interest in a corporation is known as corporate stock. This type of security is considered to be an equity security."

Let's check the options:

• a bond / an equity (Incorrect, bond is not ownership)
• a bond / a debt (Incorrect, bond is debt, but not ownership)
• corporate stock / an equity (Correct, corporate stock is ownership and is an equity security)
• corporate stock / a debt (Incorrect, corporate stock is not a debt security)

The final answer is $\boxed{\text{corporate stock / an equity}}$