A skills shortage means that there aren't enough trained workers to run a nation's businesses. This lack of skilled labor reduces the nation's GDP anywhere from 24.5% to 29%.
Skill shortages occur largely due to a lack of education. The best defense against them is a high Literacy rate, which can reduce skill shortages by up to 40%. Barring that, well-funded State Schools, large University Grants, and a high rate of Immigration can each reduce the impact of a skill shortage by up to 20%.