IFO, short for InFOrmation, is a type of DVD file that stores information about chapter, subtitles and audio tracks. IFO information is a video title set (VTS). When the disc is accessed with a DVD-ROM, you will see two directories presented: AUDIO_TS (audio title set) and VIDEO_TS (video title set).
An IFO file is one of the three types of files that are used in DVDs. From the IFO file, you can see much important navigational information, including video chapter, audio and subtitle stream, etc. IFO files are not encrypted.