zero rated supply

as per section 16 Igst

zero rated supply" means any of the following supplies of goods or services or both, namely:-

[a] export of goods or services or both; or

[b] supply of goods or services or both to a Special Economic Zone developer or a Special Economic Zone unit.

Nil rated supply

Nil rated supply is a exempted supply which is exempted by the notification

Defination of exempted supply
section 2 Cgst act
47] "exempt supply" means supply of any goods or services or both which attracts nil rate of tax or which may be wholly exempt from tax under Section 11, or under Section 6 of the Integrated Goods and Services Tax Act, and includes non-taxable supply;
so more or less exempted supply & nil rates supply is same