Employees can participate in a review cycle as Reviewees or Reviewers.
A reviewee is a person who is being reviewed or receiving a review.
A reviewer is a person who has a review to complete. A reviewer will be prompted to complete a review when visiting their profile page.
Employees may be both reviewees and reviewers in the same review cycle, depending on how your review cycle is configured. For example, a self-assessment is considered a review. If someone completes a self-evaluation, they will be both a reviewer and a reviewee.