It's a family-only celebration where the living members in each extended family honor, remember and pray for the protection of their dead elder family members (parents, grandparents, ancestors, etc...) through some special ceremonial services or rites (cleaning the person's grave, making offerings, etc, etc.). In Asian cultures they hold them either on a special national-wide holiday and/or on a series of certain consecutive anniversary dates mark the passing of time since a person's death (a few days after the person's death, then a few months later, and from then on once a year...).
So, if you have a big extended family, or your family habitualy keeps the custom by honoring each dead member for many generations afterwards, even decades after their death, then you can imagine how that would make for a very busy schedule.
Oh tyvm!!
I know I'm about to seem uncultured and all, but tf are Ancestral rites?