Fair use is a term often used in the USA – this website is aimed at the UK. When Fair use crops up it tends to be when you want to use video or music in a video/film that you are making yourself.
Youtube has a page about fair use, but this is relating to having copyright material in videos that you are making and uploading to Youtube.
https://www.youtube.com/yt/copyright/en-GB/fair-use.html