那会(nà huì) - at that time, back then in Mandarin

那会 (nà huì) points back to a past stretch of time: back then, in those days, at that time. It is the everyday spoken partner of the more written 当时, and in Beijing speech you will usually hear it with the retroflex ending as 那会儿.

In use it sits at the front of the sentence and sets the scene before anything else happens, exactly where English puts back then. 那会我还在上大学 works the same way as back then I was still at university. Its opposite number is 这会 for the present moment.

The trap for English speakers is the 会 itself. This is not the 会 that means can or will; it is an old noun meaning a moment or an occasion, and it takes a falling tone here rather than the neutral one. Reading 那会 as that will produces nonsense, so treat the two syllables as one fixed time word and move on.