Convertibility of rupee implies:

Rupee convertibility means the system where any amount of rupee can be converted into any other currency without any question asked about the purpose for which the foreign exchange is to be used.

Non-convertibility can generally be defined with reference to the transaction for which foreign exchange cannot be legally purchased (e.g., import of consumer goods etc), or transactions which are controlled and approved on a case-by-case basis (like regulated imports etc).