The complete unit that converts sunlight to electricity. Solar cells can make up solar panels, and solar panels make up a solar array. An array can be made from large amount of individual cells, but these are usually grouped into sections.
Another way to refer to an MPPT, the device that optimizes the voltage and current for the solar array (or sections of the solar array if you have multiple power trackers) so it generatres the most power. (Current x Voltage = Power, the mppt optimizes this product)