Answer:
Seasonal unemployment occurs in certain industries that are particularly affected by the change in seasons. For example, construction and agriculture. In peak seasons, like summer, these industries have increased demand for workforce, higher than in industries that are more stable yearlong.
In order to support workers in seasonally-affected industries and make sure that they will be available during the high season, the government uses a variety of unemployment compensation program. Because the work of these people simply cannot be performed during the off-season, they are compensated respectively.