or 6% unemployment, which in a given context is regarded as "normal" and acceptable. Sometimes, this rate is equated with the NAIRU. The difference between the observed unemployment rate and cyclically adjusted full employment unemployment rate is one measure of the societal level of underemployment. By Okun's Law, it is correlated with the gap between potential output and the actual real GDP. This "GDP gap" and the degree of underemployment of labor would be larger if they incorporated the roles of underemployed labor, involuntary part-time labor, and discouraged workers. Underuse of employed workers The third definition of "underemployment" describes a polar opposite phenomenon: to some economists, the term refers to "overstaffing" or "hidden unemployment," the practice of businesses or entire economies employing workers who are not fully occupied (in other words, employees who are not economically productive, or underproductive, or economically inefficient). This may be because of legal or social restrictions on firing and lay-offs (e.g. union rules requiring managers to make a case to fire a worker or spend time and money fighting the union) or because they are overhead workers, or because the work is highly seasonal (which is the case in accounting firms focusing on tax preparation, as well as agriculture and the hospitality industry). The presence of this issue in white collar office jobs is described in the boreout phenomenon, which posits that the major issue facing office workers is lack of work and boredom. This kind of underemployment does not refer to the kind of non-work time done by, for instance, firefighters or lifeguards, who spend a lot of their time waiting and watching for emergency or rescue work to do; this kind of activity is necessary in case there are multiple simultaneous incidents. This kind of underemployment may exist for structural or cyclical reasons. In many economies, some firms become insulated from fierce competitive pressures and grow inefficient, because they are awarded a government monopoly (e.g., telephone or electrical utilities) or due to a situation of abuse of market power (e.g., holding a monopoly position in a certain industry). As such, if they may employ more workers than necessary, they might not be getting the market signals that would pressure them to reduce their labour force, and they may end up carrying the resultant excess costs and depressed profits. In some countries, labour laws or practices (e.g. powerful unions) may force employers to retain