A relative reference in Excel is a pointer to a cell or range of cells. For example, a relative reference to cell A1 looks like this:
A relative addresses will change when copied to other location in a worksheet because it describes the "offset" to another cell, rather than a fixed address. To help understand what this means, consider the phrase "the house next door to the right". You can only understand the location of this house if you understand the starting point, because the location is described in relative terms.
By default, all references in Excel formulas are relative. You can convert a relative reference to absolute reference with by using dollar sign ($) characters.
In the example shown, the formula in E4 contains two relative references that will change as follows when copied down column E:
=C4*D4 =C5*D5 =C6*D6 =C7*D7 =C8*D8