Numbers 10:10

וּבְיוֹם שִׂמְחַתְכֶם וּבְמוֹעֲדֵיכֶם וּבְרָאשֵׁי חָדְשֵׁיכֶם וּתְקַעְתֶּם בַּחֲצֹצְרֹת עַל עֹלֹתֵיכֶם וְעַל זִבְחֵי שַׁלְמֵיכֶם וְהָיוּ לָכֶם לְזִכָּרוֹן לִפְנֵי אֱלֹקיכֶם אֲנִי ה' אֱלֹקיכֶם

In the day of your joy, on your holidays, and in your new months, you shall blow the trumpets over your burnt offerings and over your peace offerings. They will be a memorial for you before your G-d; I am Hashem, your G-d.

We understand what yom tov and Rosh Chodesh are, but what are these “days of joy?” The ibn Ezra explains that this refers to such as holidays as Chanukah and Purim, which the rabbis would institute in the future to commemorate victories over foreign oppressors. (It’s noteworthy that the Torah commands certain things even of rabbinically-instituted laws.)