What is the difference between raise and promotion?

I'd use them both equally, but more often raise is about raising a kid, pay rise (or pay raise) as well as raise is more about individual development, whilst promotion is more about professional growth and goods advertising

Raise is to increase your income for a better salary in the company. Promotion is an upgrade to a better post or position for a better salary in the company.

A raise is an increase in salary while a promotion is an upgrade of the individuals position in the organisation which is often accompanied by a raise of salary and additional duties.

Raises is known as  salary increase for the employees, where as promotion which is indicating to rewards of the employee by considering the management.

I'd use raise to indicate an increase in a salary or income. Where as promotion indicates an upgrade in one's job title or position in the company.