Full employment is a situation in which there is no cyclical or deficient-demand unemployment. Full employment does not entail the disappearance of all unemployment, as other kinds of unemployment, namely structural and frictional, may remain. For instance, workers who are "between jobs" for short periods of time as they search for better employment are not counted against full employment, as such unemployment is frictional rather than cyclical. An economy with full employment might also have unemployment or underemployment where part-time workers cannot find jobs appropriate to their skill level, as such unemployment is considered structural rather than cyclical. Full employment marks the point past which expansionary fiscal and/or monetary policy cannot reduce unemployment any further without causing inflation.

Some economists define full employment somewhat differently, as the unemployment rate at which inflation does not continuously increase. Advocacy of avoiding accelerating inflation is based on a theory centered on the concept of the Non-Accelerating Inflation Rate of Unemployment (NAIRU), and those who hold it usually mean NAIRU when speaking of full employment. The NAIRU has also been described by Milton Friedman, among others, as the "natural" rate of unemployment. Such views tend to emphasize sustainability, noting that a government cannot sustain unemployment rates below the NAIRU forever: inflation will continue to grow so long as unemployment lies below the NAIRU.

For the United States, economist William T. Dickens found that full-employment unemployment rate varied a lot over time but equaled about 5.5 percent of the civilian labor force during the 2000s. Recently, economists have emphasized the idea that full employment represents a "range" of possible unemployment rates. For example, in 1999, in the United States, the Organisation for Economic Co-operation and Development (OECD) gives an estimate of the "full-employment unemployment rate" of 4 to 6.4%. This is the estimated unemployment rate at full employment, plus or minus the standard error of the estimate.

The concept of full employment of labor corresponds to the concept of potential output or potential real GDP and the long run aggregate supply (LRAS) curve. In neoclassical macroeconomics, the highest sustainable level of aggregate real GDP or "potential" is seen as corresponding to a vertical LRAS curve: any increase in the demand for real GDP can only lead to rising prices in the long run, while any increase in output is temporary.