B1
used to refer to what belongs to or relates to a person when you want to avoid saying "his" or "her" or when you do not know if the person is male or female
Dictionary examples:
The chef accidentally used their phone instead of a spatula to flip the pancakes. (0.0)
The magician pulled a rabbit out of their hat, but it was actually a confused cat. (0.0)
The pirate couldn't find their eyepatch and had to use a slice of bread instead. (0.0)
So did this person give their name? (20.3)
One of the students has left their book behind. (27.1)