What's the difference between an NPO, an NPC and a trust?

An NPO is a registration, with the Department of Social Development. It says an organisation is in good standing — it does not, by itself, make anything tax deductible. An NPC is a legal form, like 'company', registered with CIPC instead: one of three shapes an organisation can take, the other two being a voluntary association (an unregistered community group with a constitution) or a trust, registered with the Master of the High Court. Most organisations on HelpLift hold an NPO registration on top of one of those three legal forms, not instead of it — the two are different questions, not different names for the same thing.