Seasonally means happening in a pattern that follows the seasons or a particular time of year. Many things in nature and human life change seasonally: deciduous trees lose their leaves seasonally in autumn, birds migrate seasonally to warmer climates in winter, and farmers plant crops seasonally in spring.

Businesses often hire workers seasonally. A ski resort might hire extra staff seasonally during winter months when skiers arrive, then let them go in summer when the snow melts. Retail stores hire seasonally before Christmas to handle the holiday shopping rush. Theme parks employ more workers seasonally in summer when schools are out and families take vacations.

The word also describes things that are only available at certain times of year. Strawberries are in season (available fresh) in late spring and early summer. Pumpkins appear in stores seasonally around autumn. When something happens seasonally, it comes and goes with reliable timing, like the blooming of cherry blossoms each spring or the return of fireflies each summer evening.