Standard Dynamic Range. It’s a term adopted to differentiate non-HDR video from HDR video.

https://en.wikipedia.org/wiki/Standard-dynamic-range_video

The quotes are there because there’s spaces in the file name. You don’t see them in the GUI because they’re not actually there. They’re added by the ‘ls’ command to help with copy/pasting of file names. You can add ‘export QUOTING_STYLE=literal’ to your ~/.bashrc to permanently suppress them, or just do ‘ls -N’ as a one off.