It's a debt  instrument, which holds a credit claim, and interest rate claim against the company.

It's an equity instrument, which has voting rights and represents a share of the company.

It's both. It's a debt  instrument, which holds a credit claim, and interest rate claim against the company. And at the same time it's an equity instrument, which has voting rights and represents a share of the company.

It's neither. It's a derivative instrument issued by the company as stock option. It allows to buy more stocks in future, and is often used as compensation for high level managers.