Is the phrase 'full employment' synonymous with the phrase 'the natural rate of unemployment'? Parkin, et al. (2010) seem to use these two terms interchangably in chapter 20, but looking up these two terms in the Oxford dictionary of economics (Black, Hashimzade & Myles 2009) shows two different meanings: Black, Hashimzade and Myles state that 'full employment' relates to the equilibrium point in the labour market, whereas 'the natural rate of unemployment' is a Keynesian concept which looks at the level of unemployment given constant inflation.
My interpretation of this is that 'full employment' is a classical concept, whereas 'the natural rate of unemployment' is not, because it seems as if the latter varies according to the rate of inflation (a nominal variable).
EDIT: The answers I have gotten so far are incorrect in that they say that 'full employment' means '100% employment'. This is incorrect because full employment actually takes into account frictional unemployment. I quote two dictionaries on the definition of full employment:
A situation where the labour market has reached a state of equilibrium, so that those in the active labour force who are willing and able to work at going wage rates are able to find work, and the only remaining unemployment is frictional unemployment.
(Black, Hashimzade & Myles 2009)
The following definition comes from The Economist
Jobs for all that want them. This does not mean zero unemployment because at any point in time some people do not want to work. Also, because some people are always between jobs, there will usually be some frictional unemployment. Full employment means that everyone who wants work and is willing to work at the market wage is in work. Most governments aim to achieve full employment, although nowadays they rarely try to lower unemployment below the nairu: the lowest jobless rate consistent with stable, low inflation.
The Economist goes on to define frictional unemployment as
That part of the jobless total caused by people simply changing jobs and taking their time about it, because they are spending time on job search or are taking a break before starting with a new employer. There is likely to be some frictional unemployment even when there is technically full employment, because most people change jobs from time to time.
In South Africa, unemployment is defined as those people who are actively seeking work, but who have not found work. Frictional unemployment seems to be a looser concept: the citizen wants work, but is happy to give up their previous job. It may be entirely possible for them to get work, just that it's taking them a while to secure their next contract. For this reason, one cannot say that an economy with a surplus of jobs is not at full employment.
Black, J, Hashimzade, N & Myles, G. 2009. Oxford dictionary of economics. 3rd edition. New York: Oxford University Press.
Parkin, M, Kohler, M, Lakay, L, Rhodes, B, Saayman, A, Schöer, V, Scholtz, F & Thompson, K. 2010. Economics: global and Southern African perspectives. Cape Town: Pearson.