Place of supply
Where, in GST's eyes, a sale happens — which decides whether you charge CGST and SGST or IGST.
Every sale under GST has a place of supply. If it is in the same state as the seller, the sale is intra-state and the tax is split into CGST and SGST. If it is in another state, the sale is inter-state and the tax is IGST.
For goods it is usually where they are delivered. For services the rules depend on the service, which is why it is printed on the invoice rather than assumed.
Learn it in a lesson
See also: CGST, SGST and IGST