A stockholder or shareholder is the holder or owner of stock in a corporation.
A stakeholder is anyone that has an interest or is affected by a corporation. In other words, the stockholder isn't the only party having a stake in the corporation. Other stakeholders in a corporation include the employees, the employees' families, suppliers, customers, community, and others.
Some organizations do not have stockholders, but have stakeholders. For example, the state university doesn't have stockholders, but it has many stakeholders: students, the students' families, professors, administrators, employers, state taxpayers, the local community, the state community, society in general, custodians, suppliers, etc.