Relative & Absolute References

By default, references are relative: they describe a position relative to the formula's cell. When you copy =B2*C2 from D2 down to D3, Excel adjusts it to =B3*C3 — "the two cells to my left, on my row."

That's exactly what you want for row-by-row calculations like line totals, and it's why you can write a formula once and fill it down a thousand rows.

Relative references go wrong only when every copy should point at the same cell — like a single tax rate or exchange rate.