To see what is actually inside the file, you must extract it using an archiving tool:

Occasionally, modders use arbitrary names for compressed assets; for example, Skyrim modders often share .rar archives containing script sources or textures.

Firmware or drivers for hardware that utilizes T27-compatible components.

Since a .rar file is a compressed archive used to group and shrink files, a file named T27.rar most likely contains one of the following: