What does the payment of tax under reverse charge mean

In terms of Section 2(98), the term reverse charge means the liability to pay tax by the recipient of supply of goods or services or both instead of the supplier of such goods or services or both under section 9(3) or (4) of the CGST Act, 2017 or under section 5 (3) or (4) of the IGST Act, 2017.

(ICAI FAQ Publication 6-9-17   LEVY AND COLLECTION: FAQ NO. 17:)