A procession in which a group of people - led by musicians and sometimes a dancer with the Shemadan - lead a bride and groom through the streets to the groom's home. More information can be found here:

http://www.orientaldancer.net/articles/shemadan.shtml

and,

According to LeylaLanty, "Zeffas for which I've played in an Arab band are usually about 8-10 minutes, sometimes longer if it's in a very large room.

As someone posted the zeffa is usually long enough for the bride and groom and their immediate families to enter the room and "process" around, then sit down. Usually, if they have a dancer for the zeffa, she leads the way for the bridal party into the room and after they are seated, she continues on to do a short performance. She may come back later in the festivities to do another solo ... or not"