heritable variation – the difference in traits among individuals of the same species that are passed down by parents

To remember the meaning of heritable variation, use the following mnemonic:

On the hairy table was the fairy's (heritable variation) inheritance from their parents. 

Heritable variation refers to the differences between individuals in a population that can be passed down from parents to offspring through genes. These variations are caused by differences in DNA sequences and are inherited through reproduction, meaning they're present in the genetic material that gets transferred from one generation to the next. 

Examples

Heritable variations include height, eye colour and hair colour.

This type of variation is important for evolution because if particular inherited characteristics give an organism an advantage in survival and reproduction, it's more likely to be passed on to future generations. Heritable variation is different from environmental variation (like scars or muscle development from exercise), which cannot be passed on to the offspring because it doesn't change the DNA in reproductive cells.