When two or more things are unrelated. when the gramatical layout of the sentence doesn't allow for the word "unrelated" the word "unrelation" can take it's place
John: This pic is getting some really unrelated arguments, "kinkyness and frozen bread" all on a pic of gemma with a leather jacket on.
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.