My guess is that you're referring to the ways in which whale song is relevant to the characters in Whale Talk.
Whales have a unique way of communicating underwater. Scientists are not exactly sure why whales "sing," but it is believed that the melodic vocalizations are used as a means of identifying each other as a form of echolocation and perhaps for the males to show fitness to the females. Far more interesting, though, is that these songs are unique to each individual. No two whales emit the same sounds, and it seems clear that whales (primarily humpback whales) "sing" even when alone.
Whale song in the novel is symbolic of TJ and his friends in a few ways. First is the idea that whales sing because they have to—it's just a form of individuality. TJ and the swim team represent the idea that being a "misfit" or an outcast can still produce beautiful things, in this case establishing that these kids are not broken, they're just different.
Second, whales are useless on land but are absolutely at home in water. Obviously the swim team doesn't live underwater, but the idea is that the pool is where they not only survive, but thrive. TJ and his "tribe" have endured heartbreak, trauma, and loneliness, but they find a family, a sense of belonging in each other because they decided to literally "dive in."
Last (for our purposes—there are plenty more examples in the book) is the idea that writers have used water to symbolize rebirth for a long time. Babies live in water for their first 9 months, but they emerge into the world as unique individuals. In many ways, the kids on the swim team are reborn in the pool. They have been bullied, treated poorly by their peers and, in some cases, by the teachers at the school, but being part of a team has affirmed that being unique is something to celebrate.