An attendee is any person who has a paid ticket. If the ticket is free, they are not counted towards the attendee count.
For example, a homeschool conference might have two ticket types. An individual ticket (for $40) and a child ticket (free). The conference might also have a family package that comes with 2 individuals and as many children as needed. The 2 individuals would count toward the attendee count but the children wouldn't (since they are free).