Symbolism, Imagery, Allegory
Yep, believe it or not Gaia is actually her own symbol. Over time, Gaia has merged with other representations of the earth (think Mother Nature). In that way, the name Gaia has become synonymous with all things earth-like.
Quick history lesson: both a scientific theory and a large-scale environmental movement have been named after our lady Gaia. In the late 1960s early 1970s chemist James Lovelock and microbiologist Lynn Margulis published the Gaia hypothesis, suggesting that the earth can be thought of as one, huge organism made up of millions of smaller organisms. Basically they suggested that because most of the things on the earth are living, we should think of the earth itself as being alive. While people were totally skeptical at first, this idea has since been adapted and incorporated into a bunch of different scientific disciplines. This idea is also one of the foundations of the Gaia Movement, an international organization dedicated to sustainability (i.e. keeping the Earth healthy – think recycling.) The United States is home to both the Gaia Foundation and the Gaia Institute, both dedicated to protecting the environment.
In popular culture, Gaia pops up all over the place. She's been a TV character, showing up both in the 1990 cartoon series Captain Planet and in more recent series like Rome and Spartacus. She's also been a video game character in games like Illusions of Gaia and God of War II. And she's a literary character in Isaac Asimov's science fiction series, Foundation. Wait, we've got one more! There's even a crater on one of Jupiter's moons named Gaia. Whew – long enough résumé for you?