The Gaia Hypothesis, presented by James Lovelock and Lynn Margulis, suggests that Earth's biosphere is actually one large organism, which they call Gaia -- pronounced various ways: GAY-ah and GUY-ah being the most common in English.
Although we may never be able to prove or disprove this hypothesis, or even find enough evidence to make it a theory, thinking about Earth's biosphere as a single life form that we are but a small part of helps us understand the inter-connectedness of all life.
Some people "worship" Gaia as a goddess and some are more scientific about the concept. As used at this website, Gaia is short for "all life on Earth functioning symbiotically as a whole." Other names include, Earth's biosphere, the ecosphere, planet Earth, Nature, the natural world, and so on.