Excel allows you to assign a name to an individual cell or a range of cells. That name can be used in a formula and can help to make the formula easier to understand.
Names can also make it easier to navigate around a large spreadsheet. In Excel 2007 and 2010, names have a scope assigned to them, meaning that a name can be a worksheet-level name or a workbook-level name.
Find out more in my easy-to-follow short tutorial: http://mthomas.co.uk/defining-and-using-range-names-in-excel/