Counter Disadvantages are disadvantages designed to cancel out advantages.
Unlike Counter Advantages (advantages designed to cancel out disadvantages) this is generally not done for the purpose of designing modifiers.
Instead the primary purpose is to do price tweaks for advantages built into traits.
Examples[]
Lilitu in GURPS Horror are built on the Spectre template (has Doesn't Eat or Drink) but to force them to eat, they have the counter disadvantage No Doesn’t Eat or Drink, which counters the DEOD advantage and removes it.