AVC stands for Advanced Video Coding (H.264). This is the compression standard used on the original discs. While newer codecs like HEVC (H.265) exist, AVC remains a highly efficient standard for 1080p content. In a REMUX, the AVC stream is untouched. This preserves the grain structure (if any) and prevents the "waxiness" that can occur when video is overly processed or compressed.