Other forms: lifespans
Someone's lifespan is the total length of time they're alive, from birth to death. The lifespan of a mosquito is much shorter than the lifespan of an elephant.
Over time, human lifespans have been getting longer and longer, as advanced medicine and nutrition keeps us healthier. In many cases, larger animals have longer lifespans — while elephants can sometimes live to be 80, houseflies generally only have a lifespan of a few weeks. In Old English, span means "distance between the thumb and little finger," or "distance between objects." Eventually the word came to also mean "length of time."