What is a Fairy Egg?

It started out like any other morning After I got my husband and kids out the door for work and school, I went out to check on my flock and collect any eggs that may be out there I was on my daily egg hunt (not all of my girls have taken a liking to nesting boxes) I was walking through the coop with a train of chickens behind me waiting for their morning treat And there, next to a few other regular sized eggs