seasonal affective disorder
noun🔊/ˌsiːzənl əˈfektɪv dɪsɔːdə(r)/
🔊/ˌsiːzənl əˈfektɪv dɪsɔːrdər/
[uncountable] (abbreviation SAD)
a medical condition in which a person feels sad and tired during late autumn and winter when there is not much light from the sun 季节性情感障碍（秋冬两季因白昼缩短而易发作的抑郁症）