This is the 40th most frequent Urdu word.
یا
"یا" means "or" in English.
The word 'یا' is used to present a choice between two options.
کیا آپ چائے پینا چاہیں گے یا کافی؟
Would you like to have tea or coffee?
The word 'یا' here is used to denote uncertainty or alternatives in a supposition.
مجھے نہیں معلوم کہ وہ آج آئیں گے یا نہیں۔
I don't know whether they will come today or not.
The word 'یا' in this sentence introduces a consequence of not performing the prior action.