The portion of sourdough starter you remove before feeding to keep the quantity manageable.
Every time you feed your starter, you're adding more flour and water. Without removing some first, you'd end up with a bucket of starter within a week. The removed portion is called discard. It's perfectly usable in pancakes, crackers, pizza dough, banana bread, and dozens of other recipes. Once your starter is mature and healthy, keep your discard in a jar in the fridge and use it throughout the week.
