Telegram is a free and open source, cross-platform, cloud-based instant messaging (IM) software. This service also provides end-end encrypted video calling,VoIP, file sharing and several other features. It was launched for iOS on 14 August 2013 and Android in October 2013. The servers of Telegram are distributed worldwide to decrease data load with five data centres in different regions, while the operational center is based in Dubai in the United Arab Emirates.Various client apps are available for desktop and mobile platforms including official apps for Android, iOS, Windows, macOS and Linux(although registration requires an iOS or Android device and a working phone number).There are also two official Telegram web twin apps – WebK and WebZ– and numerous unofficial clients that make use of Telegram's protocol. All of Telegram's official components are open source, with the exception of the server which is closed-sourced and proprietary.
Telegram provides end-to-end encrypted voice and video calls and optional end-to-end encrypted "secret" chats. Cloud chats and groups are encrypted between the app and the server, so that ISPs and other third-parties on the network can't access data, but the Telegram server can. Users can send text and voice messages, make voice and video calls, and share an unlimited number of images, documents (2 GB per file), user locations, animated stickers, contacts, and audio files. In January 2021, Telegram surpassed 500 million monthly active users.It was the most downloaded app worldwide in January 2021.
On 24 April 2020, Telegram announced that it had reached 400 million monthly active users.On 8 January 2021, Durov announced in a blog post that Telegram had reached "about 500 million" monthly active users.
Source : Wikipedia