Zero-rated means taxable at 0%; exempt means outside the charge and usually breaks input-tax recovery.
Mixed businesses may need a partial-exemption calculation because costs support both taxable and exempt activity.
Product lists and exceptions differ by jurisdiction, so confirm the classification against the authority for that supply.
The full explanation
An invoice showing no VAT can mean two opposite things, and the receipt does not say which. Zero-rated is a rate of nil with input tax recoverable; exempt is outside the tax entirely with input tax lost. A reduced rate is a third thing again — and none of the three is decided by whether something sounds essential. Read the complete guide for the reasoning, examples and definitions behind this answer.