Cashback is a refund by a bank or shop of part of the amount you spent, paid to a card or a bonus account.
In plain words
Banks and shops usually pay cashback as a percentage of a purchase: in certain categories (petrol stations, supermarkets) or during promotions. Each programme has its own terms: a monthly cap, excluded categories (often utility payments, transfers, cash withdrawals) and a payout period. Cashback may come back as money or as bonuses that can be spent only with partners. When you compare cards, look not at the headline percentage but at the cashback cap and the spending requirements.
Example. A card returns 2% on petrol-station purchases, capped at UAH 300 a month: for UAH 1,000 of fuel you get UAH 20, and the UAH 300 cap is reached only after UAH 15,000 of spending (illustrative numbers).