What does "donut hole" mean?

The empty space in the center of a donut.

What is a synonym for "donut hole"?

Common synonyms include: donuts, munchkin.

noun, slang

noun, slang ·Moderate ·College level

Noun

1
The empty space in the center of a donut.
2
A small ball-shaped pastry, made in the same manner as a donut, roughly the size of the hole in a donut. Canada, US
"These donut holes are delicious!"
3
An income bracket where one is without benefits, even though benefits are available in the next lower and next higher brackets. US, slang
"Very few younger Americans have probably ever heard of the “donut hole” in Medicare's prescription drug program, but if you're on Medicare and need expensive drugs it's likely you have."
4
A section of water for which no one has fishing rights that is completely surrounded by regions where various parties hold fishing rights.
5
The anus.

"These donut holes are delicious!"