In short: a card limit is the maximum amount you can withdraw or pay with the card per day or per transaction; you can change it in the app or at the bank.
Simply put: A limit does two jobs: a thief cannot take everything at once, and large unusual amounts get checked so that money from crime does not flow through accounts. A low limit plus a notification for every payment is the cheapest protection.
Example: You set a daily online payment limit of €100. A fraudster with your card details can take at most €100 that day, not the whole balance.
Watch out: the limit restricts not you but whoever has stolen your card. Raise it temporarily only for a big purchase.
The EU rule: for instant transfers, your bank must, on request, let you set your own maximum per day or per transaction and change it at any time (Regulation (EU) 2024/886, Article 5a(6)).
Example: Bulgaria — the same EU right applies; card limits are set in the bank's app or at a branch.
Check in your country — how your bank lets you change card and instant-transfer limits.
Source: Regulation (EU) 2024/886: https://eur-lex.europa.eu/eli/reg/2024/886/oj