A heterotroph is an organism that cannot synthesize its own food and relies on consuming other organisms for energy and nutrients. This group includes a vast array of life forms such as animals, fungi, and many bacteria. Heterotrophs play a crucial role in ecosystems as they contribute to the food web and help recycle nutrients. They obtain their energy by breaking down organic matter, leading to interactions with autotrophs, which make their own food through processes like photosynthesis.