Definition(s):

“A second subset, employees without spouses or children, has been called one of the fastest-growing segments of the workforce” (Young, 1999, p. 33).
“Clearly, there is a disconnect between the growing number of employees without children “and, within that population, the growing number of people who are single”and the limited attention that both practitioners and scholars have paid to these workers” (Young, 1999, p. 37).

Young, M. B. (1999). Work-family Backlash: Begging the question, what's fair? The ANNALS of the American Academy of Political and Social Science, 562, 32-46