You have already worked with standard formulas, functions, and cell references. Now it is time to explore the subtle but powerful concept of array formulas.

In Excel, an array can be described as a grouping of two or more cells. If you make a selection of empty cells on a worksheet, type some text or a number in one of the cells and press Ctrl + Shift + Enter at the same time, you will see the value you just typed in appear in every cell in the selection. When you press Ctrl + Shift + Enter, Excel will treat the selection as a single entity, (or array). When a selection is defined as an array, operations are performed on every cell in the selection rather than on just a single cell. You can perform operations involving corresponding cells in a number of ranges using array formulas. This is a powerful technique that can be used to enhance Excel formulas and functions.

If you enter a formula involving selections of multiple cells, and press Ctrl + Shift + Enter, Excel will automatically place curly braces { } around the formula. This means that Excel will treat this formula as an array formula. You cannot type the curly braces manually to create array formulas. They must be created by pressing Ctrl + Shift + Enter. Some people even refer to array formulas as CSE (control shift enter) formulas.