There are two camps that employees can belong to during a review cycle: Reviewees and Reviewers.
A reviewee is the person who is being reviewed.
A reviewer is the person who has a review to complete. A reviewer will be prompted to complete a review when visiting their "You" page.
Quick Note: A self-assessment is considered a review. If someone needs to complete a self-evaluation, they will be both a "reviewer" and a "reviewee."
A person is likely to be both a "reviewee" and a "reviewer" in a review cycle.