This is called a short run. Quoting from Law 18:
18.3 Short runs
18.3.1 A run is short if a batsman fails to make good his/her ground in turning for a further run.
18.3.2 Although a short run shortens the succeeding one, the latter if completed shall not be regarded as short. A striker setting off for the first run from in front of the popping crease may ...