Absolute reference

A cell reference in a spreadsheet formula that stays fixed when the formula is copied, written with dollar signs, as in $B$2. A relative reference such as B2 shifts as the formula moves; a mixed reference such as $B2 or B$2 fixes only the column or only the row.

A revenue forecast in which each year is last year's revenue multiplied by one plus a growth rate held in B2 needs that rate written as $B$2. Written as B2, copying the formula one column to the right makes it look for the rate in C2, which is probably empty. Then the forecast goes wrong with no error shown.

Mixed references are what make a two-way table possible: a discount rate fixed by row and a growth rate fixed by column let one formula fill the whole grid. In most spreadsheets the F4 key cycles through the four forms.

Fix the input; let the calculation move.