donut hole

Short definition from Wiktionary

Noun

1. 1
   The empty space in the center of a donut.
2. 2
   A small ball-shaped pastry, made in the same manner as a donut, roughly the size of the hole in a donut.
3. 3
   An income bracket where one is without benefits, even though benefits are available in the next lower and next higher brackets.
4. 4
   A section of water for which no one has fishing rights that is completely surrounded by regions where various parties hold fishing rights.