A spreadsheet is a program used for calculations involving numbers. It contains rows, columns, and cells where information can be entered and formulas can be used to perform calculations. Common spreadsheet functions allow the user to add, subtract, multiply, divide, find sums, minimums, maximums, and averages across multiple cells. Additional features include replicating formulas, using IF statements to make calculations conditional on other cell values, and inserting charts to visually display spreadsheet data.