Refers to a person who attends a formal event, especially a ceremony, funeral, or memorial service. Not used for casual gatherings.
Many attendees came to the funeral.
All the ceremony attendees were dressed in black.
参列 (attending in a line/row) + 者 (person). The kanji 参 means 'to participate' or 'to go', 列 means 'row' or 'line', and 者 means 'person'.