Also called dependent origination, inter-existence, interbeing, and no-self in Buddhist thought, the understanding of emptiness is said to be crucial for achieving the realization of enlightenment- the realization of oneness with all that is. If we are to transcend our limited view to realize the liberation of oneness, we must understand dependent origination- how everything that is manifest is "inextricably interconnected" (avinaabhava sambhandu in sanskrit, as it's put in yoga).
Everything is not only inextricably interconnected, but also free of a truly independent origination, or coming into being, is what the Buddha taught. So what does this really mean? It points to the fact that something doesn't just appear instantaneously, and it orgin goes much beyond its conception or manufacture.
Let us begin looking deeply into nature to begin understanding. First, let's look at a piece of fruit at the grocery store. Certainly, this fruit did not just appear at the grocery store. How did it come into being and come to be here at the grocery store? Well, going backwards, it was placed here by people at the store, brought here by trucks and other humans. It may have been flown into the country or trucked in from the farm. On the farm, a human picked it from a tree. The fruit grew on the tree, which produced it through pollination of its flowers, perhaps by bees. The tree, and thus fruit was nourished by rain, sunshine and all the microscopic bacteria and flora within the soil. All of the weather, wind and storms contributed to the life of the fruit. All of the interactions between insects and tree also contributed to the origination, growth and current state of the fruit. All of the nutrients in the soil affected the growing fruit. All along, from tree to grocery store, we see countless interactions between the fruit and many elements- nutrients, bugs, weather, water, tree, flower, many humans, machines and more. If any one of these factors was different, this piece of fruit would be different. Maybe its color, ripeness, size or shape would be different, or perhaps it could have been eaten sooner and we would not be holding this very same fruit as we know it. This precise fruit would not exist here and now. This fruit did not arise of itself, nor did it come from fruit as an element- it arose from countless non-fruit elements. This is the emptiness of our piece of fruit. It came into being thanks to countless interactions and potential outcomes, it exists due to this and not due to its independent "fruit-ness".
So let us look into an animal example this time, how about a scenario in nature. A bird passes away serenly. Its body its picked at by a crow, and eaten by flies, ants and smaller insects. The constituents of its body decompose by rain, sunlight, wind and bacteria working together. It becomes part of the soil, where worms eat it and enrich the earth with their castings. The rich soil feeds plant-life. The bird was never just a bird- the bird was all of these elements- sun, rain, wind, soil, plants, insects and more.
How does looking deeply reflect on a human being? Are we independent selves? We are the result of countless interactions too. To find ourself is to find the whole universe. Looking at our physical body alone shows countless interactions between the sun, rain, soil, plants, animals, farmers, machines, truckers, trucks, clerks, gasoline, boats, jets- all interacting to grow, harvest, transport and sell us our food. Our mental state or emotional level, our habits, opinions and reactions are created by all of the interactions we've ever had, all of the examples we've seen, the way others have treated us, the way it made us feel, the way we reacted to those feelings, what we've seen and read, what examples we aspire to and more. All of that depended on the ineractions our parents, neighbors and role-models had growing, their reactions, what they've learned and aspired to up that that point in time.
Looking into a tree as we see it here and now, it is made through sun, rain, snow, wind, birds, squirrels, insects, humans, soil, seasons and more. Every interaction, every intersection of phenomena effects the current state of the element we call tree. Any difference going back beyond the origin of its parent tree would impact the current manifestation of this tree. This is dependent origination.
As we see, we are not a solid, independent entity. We are all a manifestation of infinite phenomena intersecting in this particular way. Any differences in the intersecting of any or all phenomena going back well beyond the conception of our parents. If the world didn't unfold precisely as it had, here and now in this very moment we would be different somehow, thus a different being.
All exists as it is because of all else. "Because this is, that is. Because that is, this manifests. If this isn't, that is not. If that is not, this cannot be," said the Buddha. This elegant state of complete interdependence is what is known as emptiness.