Thermal printing is a specific type of ticket printer that does not require print cartridges.
The Technical Explanation;
Thermal printing is a digital printing process which produces a printed image by selectively heating coated thermal paper (ticket stock!!). When the paper passes over the thermal print head, the coating turns black in the areas where it is heated. The thermal paper is passed through the thermal head and platen. The printer then sends an electrical current to the heating elements of the thermal head, which generates heat. The heat then activates the thermo sensitive colouring layer of the thermo sensitive paper where heated - and hey presto, you've got a thermal ticket!