The tdata folder is a directory used by the Telegram Desktop application to store local authentication data, session information, and user credentials. When a user logs into Telegram Desktop, the application generates and saves encrypted files within the tdata folder, allowing users to remain logged in across sessions without re-entering credentials. The contents of this folder include cache files, configuration data, and session tokens. If the tdata folder is copied to another device, it may allow access to the same Telegram account, making it a target for attackers seeking unauthorized access. For security, users should protect and avoid sharing this folder.