Ripple is a protocol which purpose is to facilitate financial transactions. As SMTP (Simple Mail Transfer Protocol) that designed the rules which need to be followed by computers in order to tranfer e-mails, RTXP (Ripple Transaction Protocole) defines a list of rules allowing users to make transactions on the internet instantly and for free, with any currencies, cryptocurrencies or any other means.
Ripple’s goal is to link all the existing payment networks which are currently independant and require heavy backoffice to connect them. Ripple’s network is actually around 75 banks all around the world.
More here: https://www.blockchains-expert.com/en/ripple-the-protocol-that-connects-banks/