Layer shifts are when one or more printer axis shifts between layers. Instead of getting a perfect vertical shape you get a ladder shape in your model. This means that somehow that axis (X and/or Y) lost some steps along the way.
One reason for that to happen is a loosen belt. With movement, the belt will skip and the printer will start to print at a different position. Check the belt tension for the axis that is having the issue and adjust if necessary. When printing the same object more than once and if you get layer shifts in the exact same positions, then the problem can be due to a bad gcode file or SDcard.
Slice the model again and try a different SDcard. If the layer shift still occurs after all the above is checked, then get a multimeter and check the reference voltage (Vref) of the driver that has the problem.