What term describes individuals and groups, both internal and external to the company, whose support is critical to the success of the organization?

The term is stakeholder.

Explanation:

Stakeholders are the people or groups who have an interest in the business. They either affect or are affected by the business. Generally, employees, consumers, creditors, investors, and suppliers are stakeholders of a business.

Stakeholders are categorized into two types.

External stakeholders are those people or groups who are not directly related to the business, for instance, creditors and investors, suppliers.  

Internal stakeholders are those group and people who are directly related to the business, for instance, employees, owners, etc.

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