TON (TON Blockchain) stands for Telegram Open Network, which is Telegram's blockchain project. "According to the SEC’s complaint, Telegram Group Inc. and its wholly-owned subsidiary TON Issuer Inc. began raising capital in January 2018 to finance the companies’ business, including the development of their own blockchain, the “Telegram Open Network” or “TON Blockchain,” as well as the mobile messaging application Telegram Messenger."