absentee; person who is absent
Refers to someone who is not present at a scheduled event, meeting, class, etc. Neutral term.
There are three absentees from today's meeting.
We will send the materials to the absentees later.
欠席者 is a person who is absent, the direct opposite of 出席者, a person who is present.
Compound of 欠席 (absence) + 者 (person).