This article explains what an ITL file is and how iTunes uses it on your computer.

A file with the ITL file extension is an Apple iTunes database. iTunes uses the ITL file to keep track of song ratings, the files you've added to your library, playlists, how many times you've played each song, how you've organized your media, and more.

ITDB files and XML files are normally displayed along with this ITL file in the default iTunes folder.

Opening an ITL file launches iTunes, but doesn't show any information other than the media files in your library. Instead, iTunes uses the ITL file by reading/writing to it from a specific folder.