Answer:
Definition : "Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products."
Simplified : Cellular respiration is used to take in food, then is used to create ATP. ATP is a chemical the cell uses for energy. This process is called aerobic respiration. The process uses oxygen, and has four stages known as Link reaction, glycolysis, the Krebs cycle, and the electron transport chain.
You might want to re-word the simple version a little, I worded it the best I could but I used information from wiki.
