A looping schedule is when you have core subjects you teach (math, reading, writing, spelling for example), and all the other subjects rotate in between them. If you don't finish all the subjects on one day, the schedule carries over to the next day. Eventually, you've covered every subject an equal number of times.
Here's an old thread that explains it better than I probably have. http://www.welltrainedmind.com/forums/showthread.php?t=49540&highlight=looping+schedule