In Indian philosophy, your body is made up of five elements, with each of your five fingers representing one of these elements:
Thumb: fire, sun, radiant matter, heat, light – the energy that drives all other matter
Index finger: air, wind, matter in gaseous form
Middle finger: sky, space, akasha ether
Ring finger: earth, matter in solid form
Little finger: water, matter in liquid form
Most mudras are formed by using your thumb (fire) to lightly stimulate one or more of the other elements by touching its finger tip, knuckle or base.