What is the difference between Masikam and annual Tharpanam?

Masikam is the monthly ceremony performed on the same lunar tithi as the date of death for twelve consecutive months — it nourishes the soul through its post-death transition. Annual Tharpanam (Pithru Kaaryam or Abda Abdika Shradh) is the once-yearly ceremony on the death tithi after the first year. Gaya Pind Daan is neither — it is a once-in-a-lifetime act granting permanent liberation (moksha) for the ancestor. All three are distinct obligations, not substitutes for one another.