Definition
TERMINAL DATA LINK SYSTEM (TDLS)
A system that provides Digital Automatic Terminal Information Service (D-ATIS) both on a specified radio frequency and, for subscribers, in a text message via data link to the cockpit or to a gate printer. TDLS also provides the CPDLC Departure Clearance Application (DCL) and Pre‐departure Clearances (PDC), at selected airports, to subscribers, through a service provider, in text to the cockpit or to a gate printer. In addition, TDLS will emulate the Flight Data Input/Output (FDIO) information within the control tower.
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).