Kairos is a Greek word meaning something like "Opportunity" or "Chance." It was a word for time when something special could happen.
Kairos was the god of the fleeting moment. He was always on his feet, often depicted with wings, and he carried a razor, reminding us of the sharp and quick nature of opportunities.
Most notable about Kairos was that he had long bushy hair on the front of his head over his face, but the back of his head was completely bald. The idea is that you can grasp an opportunity as it arrives, but once it's past you, there's nothing you can do about it.
This all gave rise to the expression, "Opportunity is bald from behind."
Kairos is a word that shows up a lot. There is a church planting group led by one of my professors, Stan Granberg called "Kairos." The idea is that we need to be seizing the opportunities around us to reach people for Christ. I think this is a helpful allusion, if not a great sermon illustration.