Multiplexing is the act of aligning multiple video, audio, and subtitle tracks in paralleled in a data stream to allow them to be all read concurrently. REMultiplexing is manipulating those streams to rearrange them. I do not 'rip' discs as you understand it, where a lossy video compression process is done, usually to yield smaller files. When you REmultiplex a disc you COPY the video, audio and subtitle data. It is NOT recompressed and there is no loss. It is a LOSSLESS process and vast as it only copies data. That means all the AV data in my MKVs are IDENTICAL to that on the disc, just cut up into individual episodes for ease of access.
This is ALSO how I can take the remultiplexed rip of the CCS movie and then INJECT an additional audio stream from the DVD to give it a second dub track. It writes a new file with the additional streams.