Today’s homework is to make an explanation of what Obon is in English.
盆 refers to either the lantern festival or a tray. The お just makes it higher status. The meanings stay the same, though. So, depending on the context, this means Lantern Festival, aka obon and obon festival, or a tray.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.