A "Cryptocurrency swapper" is a service that swaps one type of cryptocurrency for another.
It is basically the same as buying and selling from exchanges for fiat, except that you only get fiat.
Swappers are in general able to receive send coins from any address, including self custody addresses.
Centralized swappers were a good way to workaround the endless Monero bans from exchanges circa 2024, e.g. x.com/cirosantilli/status/1771900725649371240 as they effectively serve as proxies for exchanges that are still legal in other countries.
They will eventually have to ban Monero of course, and then the only way left will be decentralized exchanges.
This leads to a scenario where the only effective way to ban Monero is to also ban all other cryptocurrencies. The question is if countries will go that far or not.