Stands for Advanced Video Coding (H.264), the compression standard used for the video stream.
This is the highest quality available. A "Remux" takes the raw video and audio streams directly from the physical Blu-ray disc and puts them into a digital container (like .mkv) without re-compressing the video. This preserves the original disc quality perfectly.
If you are looking to watch the film legally, you can find it on several major platforms:
Refers to Dolby Digital 5.1 surround sound, providing immersive audio with five full-bandwidth channels and one low-frequency effects channel. Where to Watch Officially