professional development day
noun🔊/prəˌfeʃənl dɪˈveləpmənt deɪ/
🔊/prəˌfeʃənl dɪˈveləpmənt deɪ/
(abbreviation PD day)
(especially Canadian English) (British English inset day)
a day on which classes at schools are cancelled so that teachers can get further training 专职进修日，教师发展日（学校停课）