Wedding Ceremony Prelude music is the music you play as guests arrive. When you are booking DJ services typically most ceremonies are 30 mins long and you want to book your DJ 30 minutes before that time as you want music playing as guests arrive. This is also gives some time for the DJ to put a microphone on the officiant and test sound as most officiants arrive a few minutes before ceremony start time.
Prelude music can be anything you want it to be now a days. Typically prelude music is classical music either piano, string guitar, violin, and in some cases harp. More and more we are seeing Brides and Grooms step away from tradition and put their own spin on things. Examples would be taking modern pop songs and having an instrumental version of that song. Popular artists such as Vitamin String Quartet, Piano Guys, and more. Some Brides and Grooms have asked for instrumentals with movie theme songs or popular Disney songs. We also have done a few ceremonies with Jazz.
Here are a few examples of Prelude style of music. As mentioned this is not the end all be all.