structural unemployment

The idea that a certain percentage of the unemployed work force have no skills that can be used productively by employers.

Structural Unemployment and Frictional unemployment account for approximately 4.5% of the unemployed work force, and is excluded from calculating Potential GDP. Therefore, if there is 7% of the work force unemployed at a particular time, roughly 4.5 percentage points of that 7% is either frictionally or structurally unemployed and not truly available to work. Therefore, the economy is actually operating at about 2% less than full employment potential.

Note that in the United States at least, there is an additional wrinkle when computing unemployment. A person is considered unemployed if and only if they are looking for a job. And, even if they are looking for a job, after a certain amount of time looking without luck, they are no longer considered as among the unemployed. I think this group might be lumped in with those in the structurally unemployed category, but it is not necessarily because they have no useful skills.

It might just be because they are unlucky.