The term for a mammal that lays eggs is "monotreme." Monotremes are a unique group of egg-laying mammals distinguished from other mammals, which generally give live birth. The most well-known monotremes are the platypus and the echidnas, or spiny anteaters. These fascinating creatures possess a mix of mammalian and reptilian features, including the ability to lay eggs instead of giving live birth. Monotremes are primarily found in Australia and New Guinea, and they represent a small branch of the mammalian lineage, showcasing the diversity in reproductive strategies within the animal kingdom.