Mock turtle soup was a popular dish in Victorian England made from calf's head and other inexpensive meats, meant to mimic the flavor of turtle soup, which was a luxury food at the time.
In "Alice's Adventures in Wonderland," the Mock Turtle is a sad and wistful character who sings a song about his "tears" and reminisces about his past life as a real turtle. His name is a direct reference to the imitation soup, further emphasizing his melancholy and the sense of being a counterfeit or imposter.