Lehmer (1951), by way of Knuth Vol. 2, "A random sequence is a vague notion embodying the idea of a sequence in which each term is unpredictable to the uninitia

Lehmer (1951), by way of Knuth Vol. 2, "A random sequence is a vague notion embodying the idea of a sequence in which each term is unpredictable to the uninitiated and whose digits pass a certain number of tests, traditional with statisticians and depending somewhat on the uses to which the sequence is to be put."