This is a variation of a straight arm Lat Pulldown with the added element of a slight row. This exercise will isolate your lats and is an excellent exercise to do after pull-ups or lat pulldowns to really get them fired up.
This can be performed from standing or kneeling. If standing you will need to be able to perform a hip hinge and maintain that position.
If you have not tried this movement before try the standard straight arm version first before progressing to the J-Pulldown.