Definition of randomness : the quality or state of being or seeming random (as in lacking or seeming to lack a definite plan, purpose, or pattern) … the metaphor of a coin flip for randomness remains unquestioned. We use coin tosses to settle disputes and decide outcomes because we believe they are unbiased, with 50-50 odds. Yet recent research into coin flips has discovered that the laws of mechanics determine the outcome of coin tosses … — David E. Adler the randomness of life