The term "cash advance" is a catch-all for "cash-like" transactions. Deep in its T&Cs Halifax specifically mentions:
Cash withdrawals – which can mean using an ATM or, say, getting cashback at the supermarket.
Buying foreign currency – in other words using your card at a bureau de change to pay for foreign currency.
Gambling transactions – which was banned on credit cards anyway as of April 2020. Bear in mind that any transactions (buying drinks, for example) in gambling establishments such as casinos or betting shops are liable to be treated as cash advances.
The Clarity's cash advance fee is 0% but you will start paying interest on these transactions from the day they take place – even if you always pay your full balance off each month.