NISA stands for new ISA. It is a variant of the individual savings account that was brought in by the Chancellor of the Exchequer at the time, George Osborne, in 2014.
A NISA had a higher annual limit than the ISAs that preceded it, and allowed savers to transfer previous ISA balances from cash ISAs to stocks and shares ISAs, or the other way round. NISA’s also allowed a wider range of investments to be held within the tax wrapper account that its predecessors. The term NISA is now defunct as these are just known as ISAs once more.