How Excel selects a region?

A region is a group of cells with data and is bounded by blank cells around it (or) a block of cells that includes the currently selected cell or cells and is bounded by blank columns and rows.. To identify a region in a group of cells, click a cell and press CTRL + SHIFT + *. Press the * that is above the number 8 and not the * in the number pad.
For the sake of explanation, we will enter blank cells as well. Also, we will add data in cells as we go along:
Enter 1 in cell D3, and 1 in cell E4. Click cell D3 and press CTRL + SHIFT + *. Cells C2 to F2, C3 to C5, D5 to F5, and F3 to F4 are all blank. So, the region is D3:E4.

Add 1 in F5. Click cell D1 and press CTRL + SHIFT + *. You will see the region in the following in the following figure because the cells around, i.e., C2 to G2, C3 to C6, D6 to G6, G3 to G5 are all blank cells.

In the following figure, we add 1 in G2, 1 in D6, 1 in G7. Click cell D1 and press CTRL + SHIFT + *. You will see that G2 was blank in figure 1 but now it is not blank and so it is included in the region. Similarly, D6 is not blank now and is included in the region. With the region spanning across D2:G6, cells around D2:G6 should be blank but G7 has the data 1 and so it is included in the region. The region now spans from D2:G7.

We will add data in 3 more cells. We add 1 in cell B9, 1 in cell C8, and 1 in cell G10. From the figure above the region spanned from D2:G7. Click cell D1 and press CTRL + SHIFT + *, you will see that the region now spans from B2:G10.

Generally a region must have filled cells. The example was to show how Excel selects a region. In this example, the region was from B2:G10. If there are plenty of blank cells then it is not true that the same region will appear if you click other cells and press CTRL + SHIFT + *. For instance, try clicking B9 or B7 or D6 or any cell from B2:B6 and press CTRL + SHIFT + *.