IPA: /ˈreɪtər/
KK: /ˈreɪtər/
A person or thing that assigns a score or value to something based on a set of criteria.
The rater evaluated the performance of the students during the exam.
Rater → It is formed from "rate" (from Old French *rate*, meaning to estimate or assess) and "-er" (meaning a person who). A rater is a person who assesses or evaluates something.
Think of someone who 'assesses' ('rate') something — the '-er' just means a person. A rater is someone who evaluates.