determiner / pronoun / adverb
that
THAT/ðæt/
Points to something identified or more distant.
The customer points to that green mug in the shopkeeper's hand.

Etymology
The Old English demonstrative singled something out. Originally restricted to neuter nouns, it later applied to any gender, retaining its role of identifying a particular person or thing.
In context
At that time, we started a movement,
At that point, they changed the instructor.