What is Microsoft Excel?

Microsoft Excel is an electronic spreadsheet program.

You might of heard the terms "spreadsheet" and "worksheet". People generally use them interchangebly. To remain consistent with Microsoft and other publishers the term worksheet refers to the row-and-column matrix sheet on which you work upon and the term spreadsheet refers to this type of computer application. In addition, the term workbook will refer to the book of pages that is the standard Excel document.The workbook can contain worksheets,chart sheets, or macro modules.
The Spreadsheet Concept

The Workbook

Most of the Excel screen is devoted to the display of the workbook. The workbook consists of grids and columns. The intersection of a row and column is a rectangular area called a cell.

Cells

The workbook is made up of cells.There is a cell at the intersection of each row and column.A cell can contain a value, a formula, or a text entry. A text entry is used to label or explain the contents of the workbook. A value entry can either be a constant or the value of a formula. The value of a formula will change when the components (arguments) of the formula change. The appeal of spreadsheet programs is the ability to change one value and watch all other values that depend on that first value automatically change when the spreadsheet is recalculated.

Rows, Columns, and Sheets

The Excel worksheet contains 16,384 rows that extend down the worksheet, numbered 1 through 16384.

The Excel worksheet contains 256 columns that extend across the worksheet, lettered A through Z, AA through AZ, BA through BZ, and continuing to IA through IZ.

The Excel worksheet can contain as many as 256 sheets, labeled Sheet1 through Sheet256. The initial number of sheets in a workbook,which can be changed by the user is 16.

Cell References

Cell references are the combination of column letter and row number. For example, the upper-left cell of a worksheet is A1.

Source: http://einstein.cs.uri.edu