So "WEB" isn't a format at all. I'm not an expert, but I'll have a go at explaining the situation using the sources that I've found helpful.
"Remuxing is the process of transferring the video and audio streams from one container file to another container without any alteration to the streams’ quality. The video and audio in the new container will be identical to that in the original file, but in a different container format.
The main difference between a remux and a re-encode is that a remux only changes the container format, while a re-encode compresses the video and audio streams, which can result in a loss of quality.
Remuxing allows for a smaller file size without sacrificing quality, making it ideal for archiving or distributing large video files.
A container file, also known as a wrapper or a file format, is a type of metadata that contains various types of data, like video, audio, and subtitles tracks, that are encoded with a codec."
"Remuxing can lead to a reduction in file size as only the main video and one of the original soundtracks are preserved in their original form, while all other data, such as additional audio tracks, subtitles, or chapters, can be removed."
HEVC = H.256
AVC = H.264
As I understand it - the difference between x265 and H.265 is that H.265 is the compression standard and x265 is the software most pirates use - because these compression standards are copyrighted.
WEB Dl = Downloading the file from the source, as is. Aka you get the same file the website has.
WEB RIP = Downloading thr file from the source, but it might be compressed by the server that serves you the file (aka if you download a file from FB you get a compressed POS file that looks like butthole)
Edit: x265 is more efficient than x264 - so the file size is less , but it requires more processing power to run the files (aka if you're using a raspberry pi as a media server you might want to go with x264 rather than x265 purely due to the processing power required to run x265 - even though the file size is smaller for x265
So if you WEB DL a file that has multiple languages of audio, and different subtitles- you might remux it so it has only English audio and Engligh subtitles - the English audio and subtitles will be the same size as they originally were, but you will get rid of everything else that you don't want.
You could then re-encode it to compress the file so that it's smaller. You coukd re-encode it first if you wanted to - but you would be compressing all of the audio and subtitle files when most people don't need that.