Solar cell = by look it appear as square or pseudo square, by color it is blue, dark color with or without metal lines on the top. It is an electrical device that can convert sun into electricity. A basic solar single junction solar cell can produce Voc in the range of 0.6V to 0.7.
Solar cell string = referring to multiple solar cells connected in series.
Solar module = referring to solar string layered with polymer for protection and packed into a metal frame. Solar module can be equipped with either full solar cell or half solar cell. The traditional standard full cell can have 36 cells per module, 60 full-cell or 72 full-cell per module. But now, the traditional format is transformed 120 half-cut or 144 half-cut cell per module.
Solar Array = referring to multiple solar module that is connected either in-series or in-parallel to create a solar system that you can use it for house application, buildings and even solar farm.