  Ability to generate random numbers is an important resource for many
applications ranging from scientific research to practical cryptography and
quantum technologies. However, a widely accepted definition of random numbers,
or randomness, has eluded researchers thus far. Without a definition, it is
impossible to complete security proofs or make new industrial standards. Here,
we propose an information-theory-based definition of randomness which, unlike
state of the art, does not try to find desirable properties of generated
numbers, but rather focus on the physical process of random number generation.
We explain its intuitiveness, demonstrate its verifiability and further define
randomness deviation as a measure of quality of the random number generating
process or device.
