In (quantitative) genetics literature, heritability is usually defined (simplifying a bit) as the proportion of variance of a trait (lifespan, height, etc), in a population, that can be explained by genetics. The rest, by environmental factors, or error.
If height were a 100% heritability means that all differences in height between individuals would be explainable by genetics.
If height were a 100% heritability means that all differences in height between individuals would be explainable by genetics.