What is swap app?

Excuse me, could you please clarify what exactly is meant by "swap app"? Is it a type of financial application that facilitates the exchange or swapping of cryptocurrencies or other digital assets? If so, how does it work? Does it allow users to trade one type of asset for another in a seamless and efficient manner? Are there any fees associated with using such an app? And most importantly, is it SAFE and secure to use for managing one's digital assets? I'd appreciate any insights you may have on this topic.