Zero Rate Tax

I think it means if they were taxed at normal rate it would increase cost of essential goods such as basic foods to lower income/wealth people. Hope this helps.

Quite correct. In addition VAT is a regressive tax meaning that it impacts more on less well-off people. If someone spends £1,000 (before VAT) on food in a period. If food were standard rated at 20% then their costs would increase by £200. If the person had a salary for the period of £2,000 then the extra £200 is a lot (10% of income) compared to its effect on someone earning £5,000 (4% of income).