Die off is a term used to describe a sudden decrease in the population of a species due to environmental factors. It is often caused by a lack of food, disease, or other environmental changes that make it difficult for the species to survive. The term PERISH, which is a synonym for die off, is used to describe the death of an individual organism or a group of organisms. In some cases, die off can be caused by human activities such as over-hunting, pollution, and habitat destruction.