used as a relative pronoun to introduce a part of a sentence which refers to the person, thing or time you have been talking about
که, چیزی که, زمانی که, شخصی که, کسی که
Where's the letter that came yesterday?
Who was it that won the US Open?
The watch (that) you gave me keeps perfect time.
The people (that) I spoke to were very helpful.
It’s the best novel (that) I’ve ever read.
We moved here the year (that) my mother died.