Forensic entomology is a sub-type of Forensic Science. It deals with study of arthropods that resides in corpse. It helps to determine time of death of corpse. You should also check post of @Daniel Sumner on this topic. His post is very informative.
Forensic entomology employs the use of insect behaviour and lifecycles to help answer questions that apply to forensic settings. Some of the questions might relate to when or how long a dead body has occupied a space. Knowledge of when insect or larvae hatch or change and the timeline helps assist in determining length of time a dead body has been in the open.
Entomology itself finds its roots within the Greek 'entomon' and meant "cut up in pieces" or "having a notch cut at the waist" (Etymology online 2022).
Entomology should not be confused with etymology whice refers to the origin of words.