Final answer:
The small green square used to copy formulas or data in adjacent cells is called the Fill Handle. You click and drag it to replicate content in other cells in a spreadsheet.
Step-by-step explanation:
The small green square in the lower-right corner of a selected cell that you use to copy a formula down or to auto-fill data in adjacent cells in a spreadsheet application like Microsoft Excel is known as the Fill Handle. To use it, you first select a cell with a formula or data you want to copy. Then you click and drag the Fill Handle down or across to the other cells where you want to replicate the formula or extend a series of data.