This really is the realm of Google and WikiPedia.
Standard DVDs use compressed lossy sound. It's similar in compression to 128 kbps mp3 if you're talking about AC3 (640 kbps over 6 channels). DTS can have double that bitrate. IN the HD video formats, both Dolby TrueHD and DTS-HD Master Audio are lossless formats, but compressed of course. You can rip BLuRays to h264 video, and multi-channel FLAC audio containing mkv files, and get both great video and lossless sound to your AV receiver.