What exactly is Yom Tov? and why are some holidays Yom Tov and some others not (like CHannukah)

I didnt grow up in an observant family and I’m currently trying to learn more about the traditions and holidays I didnt take part in growing (only celebrated Hanukkah). I recently came across the word ‘Yom Tov’ and I’m a bit confused by what it is exacly. On Chabad’s site it says Yom Tov includes dates such as the first and last day of Passover, Shavuot, Rosh Hashanah, Sukkot and Shemini Atzeret. Is Yom Tov basically a holiday where you can’t do ‘work’ like Shabbat? Hence why Hanukkah isn’t Yom Tov? If yes then what defines what days/holidays are and arent Yom Tov.