A TMOD file is a mod created by tModLoader, a program used to create and distribute mods for Terraria, a 2D sandbox construction action and adventure game. It contains a mod compiled from mod source files, such as .CS and .PNG files. TMOD files are used to add or alter content in Terraria.

The TMOD file is created by tModLoader to store a user's mod. You can open the location of your TMOD files from the tModLoader main menu. Click Mods in the main menu, then click Open Mods Folder, which will display the location of your mods. If you want to install another users' mod, copy the TMOD file and save it in your "Mods" folder. In order to install tModLoader, download the utility and copy it into the Terraria Steam install folder. It is most likely found in the following directory: C:\Program Files (x86)\Steam\SteamApps\common\Terraria