Telegram is a cloud-based messaging app with one-to-one chats, groups and broadcast channels, with messages synchronised across a user's devices. Cloud chats are encrypted between the app and Telegram's servers and stored in the Telegram cloud. End-to-end encryption applies to optional secret chats, which stay on the device where they were started, and to calls.
Telegram's development team is based in Dubai in the United Arab Emirates, and its group companies are located in the British Virgin Islands and Dubai. According to its privacy policy, data of users who signed up from the EEA or the UK is stored in data centres in the Netherlands, and Telegram acts as data controller, with a representative in the EU under the GDPR. The client apps are open source, while the server code is not published. For a European organisation this means a non-EU provider outside US jurisdiction, but also a closed server side, so cloud chats are not end-to-end encrypted.