This is short for “environmental DNA.” DNA encodes the genetic instructions for living things. It’s found in nearly every cell of everything from bacteria to humans. eDNA is shed by organisms into their environment. Scientists can find that DNA in samples they collect from an environment. They can then decipher the molecular sequences in that DNA. Every species has different DNA, so those sequences can be used to identify who’s around.
In a sentence
Animals may walk, run, swim or fly away, but they’ll often leave some eDNA for scientists to find.