What is a Yellow sea feeder?

A feeder in table-tennis terminology refers to a topspin ball that falls short so that it bounces twice (or more) on the table. If the ball's first landing on the table is near the corner of the table (i.e., the area covered by the 4ft x 4ft yellow square marking), it is called the yellow sea feeder. These balls are quite challenging to return. This is because if you take the ball early after it bounces once on the table, the ball tends to fly high after the second bounce. On the other hand, if you decide to take the ball after the second bounce, it becomes relatively slow (due to the friction with the table) and tends to be hit short.