expression, noun, noun which may take the genitive case particle 'no'
at that time; in those days; then
Refers to a specific past time or period previously mentioned or understood from context. Can be used as a noun or adjectivally with の.
その頃、私はまだ学生でした。
At that time, I was still a student.
その頃のことはよく覚えていない。
I don't remember much about those days.