Wikipedia defines the word as thus, "Ubuntu is a Nguni Bantu term meaning "humanity." It is often translated as "I am because we are," or "humanity towards others," but is often used in a more philosophical sense to mean "the belief in a universal bond of sharing that connects all humanity."
I have heard it described by this illustration, "An anthropologist proposed a game to the kids in an African tribe. He put a basket full of fruit near a tree and told them that whoever got their first won the sweet fruits. When he gave them the signal to run they all took each other's hands and ran together, then sat in a circle enjoying their treats. When he asked why they chose to run as a group when they could have had more fruit individually, one child spoke up and said, 'UBUNTU, how can one of us be happy if all the others are sad?'"
Jesus spoke a parable that parallels this philosophy. Matthew 20 tells us the parable of the vineyard workers who come in to work at different times of the day, but, at the end of the day, each worker is paid the same. This angers the workers who spent more hours on the job. They didn't understand what Jesus had shared earlier in the last verse of Matthew 19, "But many that are first shall be last; and the last shall be first." UBUNTU, we are the same, equal; therefore we shall share the kingdom together, just as the children in the illustration shared their tasty reward. How could we be happy if everyone else is sad?
In God's eyes we are all His creation, no matter the color of our skin, the place we may live, or the wealth we may obtain. The world would be a much better (and happier) place if we could grasp this concept.