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.
Today’s homework is to make an explanation of what Obon is in English.