Ball
Dance
noun
A dancing (舞踏) meet is when you all get together to do dancing, the kind that's like "step step swing" (or whatever). This is a ball or dance.
ぶとうかい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
今回の舞踏会には、前回よりも明るい色のドレスを着て行くつもりです。
For this dance, I’m thinking of wearing a brighter color dress than the last time.