Unemployment, according to the OECD (Organisation for Economic Co-operation and Development), is people above a specified age (usually 15)  not being in paid employment or self-employment but currently available for work during the reference period.Unemployment is measured by the unemployment rate, which is the number of people who are unemployed as a percentage of the labour force (the total number of people employed added to those unemployed).Unemployment can have many sources, such as the following:

new technologies and inventions
the status of the economy, which can be influenced by a recession
competition caused by globalization and international trade
policies of the government
regulation and marketUnemployment and the status of the economy can be influenced by a country through, for example, fiscal policy. Furthermore, the monetary authority of a country, such as the central bank, can influence the availability and cost for money through its monetary policy. In addition to theories of unemployment, a few categorisations of unemployment are used for more precisely modelling the effects of unemployment within the economic system. Some of the main types of unemployment include structural unemployment, frictional unemployment, cyclical unemployment, involuntary unemployment and classical unemployment. Structural unemployment focuses on foundational problems in the economy and inefficiencies inherent in labor markets, including a mismatch between the supply and demand of laborers with necessary skill sets. Structural arguments emphasize causes and solutions related to disruptive technologies and globalization.
The effect was particularly pronounced for those with vocational or secondary education.Costs of unemployment also vary depending on age. The young and the old are the two largest age groups currently experiencing unemployment. A 2007 study from Jacob and Kleinert found that young people (ages 18 to 24) who have fewer resources and limited work experiences are more likely to be unemployed. Other researchers have found that todays high school seniors place a lower value on work than those in the past, which is likely because they recognize the limited availability of jobs. At the other end of the age spectrum, studies have found that older individuals have more barriers than younger workers to employment, require stronger social networks to acquire work, and are also less likely to move from temporary to permanent positions. Additionally, some older people see age discrimination as the reason for them not getting hired. Social
An economy with high unemployment is not using all of the resources, specifically labour, available to it. Since it is operating below its production possibility frontier, it could have higher output if all of the workforce were usefully employed. However, there is a tradeoff between economic efficiency and unemployment: if all frictionally unemployed accepted the first job that they were offered, they would be likely to be operating at below their skill level, reducing the economys efficiency.During a long period of unemployment, workers can lose their skills, causing a loss of human capital.