There are three main types of unemployment: cyclical, frictional and structural. Cyclical unemployment occurs because of the ups and downs of the economy over time. When the economy enters a recession, many of the jobs lost are considered cyclical unemployment.
Frictional unemployment occurs when workers leave their old jobs but haven't yet found new ones. Most of the time workers leave voluntarily, either because they need to move, or they've saved up enough money to allow them to look for a better job.
Structural unemployment exists when shifts occur in the economy that creates a mismatch between the skills workers have and the skills needed by employers.
An example of this is an industry’s replacement of machinery workers with robots. Workers now need to learn how to manage the robots that replaced them. Those that don't learn need retraining for other jobs or face long-term structural unemployment.
A long recession often creates structural unemployment. If workers stay unemployed for too long, their skills have likely become outdated. Unless they are willing and able to take a lower-level, unskilled job, they may stay unemployed even when the economy recovers. If this happens, structural unemployment leads to a higher rate of natural unemployment.
Cyclical unemployment is not part of the natural unemployment rate. It's caused by the contraction phase of the business cycle. That's when demand for goods and services fall dramatically, forcing businesses to lay off large numbers of workers to cut costs.
Cyclical unemployment tends to create more unemployment. This is because the laid-off workers have less money to buy the things they need, further lowering demand.