The 'die' corresponds to the final product being made, but to make it, multiple die are fabricated on a planar, circular 'wafer', and these wafers are often grouped into 'lots' (typically 24 wafers in a lot). When all the steps required to fabricate the product are completed, all the die on each wafer are tested to see how well they work. Although potentially complex, the end result of this test is that each die is assigned to a 'bin' (some bins being considered 'passing', and some bins 'failing'). To make functioning products, each wafer is sawn up (between the die), and passing die are assembled and packaged. Generally, only one product type is fabricated on each wafer, so the goal is to process that wafer at each step in such a way that all the die on it are, nominally, identical.
Try searching for 'semiconductor fabrication' or 'wafer fabrication'.