An attendee is a person who shows up at an event or meeting. If you go to your family reunion every summer, you can say you're a regular attendee.
Conferences, conventions, and other gatherings need to have attendees so they can proceed as planned. You might be a French club attendee at school or a regular town bike swap attendee. The original word for attendee was attender, but its meaning came to be "someone who waits on others," while attendee, as of the mid-20th century, was "someone who attends."