A season or time of year (e.g., spring, summer, autumn, winter); a period within the year.
日本の春の季節は桜が美しい。
In Japan, the spring season has beautiful cherry blossoms.
季節ごとに食べられる果物が変わる。
The fruits you can eat change with the seasons.
季節の変わり目は体調を崩しやすい。
You tend to get sick when the seasons change.