attendee
A person who goes to and is present at an event.
An attendee is someone who goes to an event, meeting, or gathering. If you attend your cousin's birthday party, you're an attendee. Students at a school assembly are attendees, and so are the hundreds of people who show up for a big conference or concert.
While “attend” focuses on the action of going, “attendee” describes the person doing it. Conference organizers count attendees to know how many chairs to set up. Event planners track attendees to make sure everyone who registered actually shows up.
You'll often see this word in more formal contexts. A teacher might call you a “student” rather than an “attendee,” but if your school hosts a special workshop, suddenly everyone there is an attendee. The word works for any size gathering: two attendees at a small committee meeting or fifty thousand attendees at a championship game. What makes someone an attendee isn't how important they are, but simply that they showed up.