Today is Eid Al Adha, a holiday celebrated in Islam. It means the Festival of Sacrifice. My understanding from friends is that they do this to remember when Abraham was going to sacrifice his son, but God provided a sacrafice in the son’s place (see here) In many places in the world a goat will be sacrificed and meat will be given to the poor. It’s a good reminder for me to remember God’s mercy and an awesome reminder of God’s love in the ultimate sacrifce for me, Jesus.
So if you run into any Muslim friends today congratulate them by saying Eid Mubarak (which basically is like saying Happy Holidays!).