Muslims celebrate the holiday to commemorate their belief in Abraham's willingness to follow God's command to sacrifice his son Ishmael, and Ishmael's consent to being sacrificed. Today, it is is marked by slaughtering animals to feed the poor. There is a discrepancy here, Abraham was to sacrifice his son, Isaac, not Ishmael. Isaac consented to the sacrifice and Abraham started to do so when stopped by God.
There may be some Muslims on here who celebrate this day, but very few I would imagine.