Relative age is a method or technique of dating rocks and rock units called strata.
Relative age or dating does not really give the actual age of something, but it does put things in sequential order. This allows geologists to determine the age of a rock or strata relative or in comparison to another rock.
Therefore instead of stating when something happened, it puts events in the order that they happened. Geologists use a variety of techniques to determine the relative age of a rock unit.