What does a #NAME? error signify, and what are the common reasons for it?

A #NAME? error indicates that Excel doesn't recognize something in your formula. The most common reasons are: 1) Misspelled function names (e.g., 'SUMM' instead of 'SUM'). 2) Using a named range that doesn't exist or is misspelled. 3) Enclosing text in quotes incorrectly (text in formulas usually needs quotes, unless it's a named range or function). 4) Forgetting a colon in a range reference (e.g., A1 A5 instead of A1:A5). Review the spelling of all functions and named ranges used in the formula.