It means an organism respire without it
so that organism know as anaerobic
for example : bacteria eats human and animal dead bodies under the earth there O² is deficient so bacteria respire with oxygen O²
Dinosaur fossils had been known for centuries as "dragon bones" or the remains of giants, but it wasn't until Dean William Buckland of Oxford, England described the carnivorous "lizard" Megalosaurus<span> (in 1824) that they were formally studied as an extinct group of giant reptiles</span>
Zebra,Blackbear,butterfly,pandabear