Baggage limit per piece/per weight or pet person?

Hi,

I got an international flight lined up from Istanbul to Birmingham. The check in baggage limit is 30kg.

I wanted to ask is it limited to just 1 suitcase of 30kg or are you allowed to

for example check in 2 suitcases of 15 kg each for example check in 3 suitcases of 10 kg each

Anyone know what the rules are for this?

Thanks.