The number 84 is a classical number given to how many yoga postures there are. This is due to the fact that there are 84 lakhs (100,000 which = 8.4 million) species which include: 3,000,000 types of plants and trees, 2,700,000 types of reptiles and insects, 1,400,000 kinds of aquatic animals and birds, 900,000 varieties of mammals and 400,000 types of humans, gods, goddesses and disembodied spirits.
The names of the postures illustrate the universal principle of consciousness in different stages of evolution. By practicing the classical positions of man/woman and nature one helps to universalize consciousness.