Step 1: Meaning.
When a non-trading organisation receives subscription for the next year in advance, it has not yet been earned.
Step 2: Why liability?
The organisation is obliged to provide services in the next year for which subscription is already received. Until then, it remains an unearned income.
Step 3: Treatment.
Hence, subscription received in advance is shown as a liability in the Balance Sheet.
Final Answer:
\[
\boxed{\text{Liability}}
\]