Type a word, then add flags. /verb /noun /adj /adv prefer that use of the word in the caption (English looks at a few words of context; Japanese uses the learner dictionary). /ask keeps questions; /exclaim keeps exclamations. /male and /female look at title and channel cues, and keep unknown speakers if too few clips are tagged.
topic:travel matches the topic in the title, channel, or caption. in:VIDEOID limits to one video. ch:UCchannelId limits to one channel. /mix shuffles the ranked list. Accent chips on the player pass a region into YouTube expand and prefer titles that name that variety.
Filters live on the home-page Filters dialog and in the query string, so a shareable /hear/… URL keeps the same constraints.