This reflects all the genetic contributions to a population's phenotypic variance including additive, dominant, and epistatic (multi-genic interactions), as well as maternal and paternal effects, where individuals are directly affected by their parents' phenotype (such as with milk production in mammals).
David Rowe reported an interaction of genetic effects with Socioeconomic Status, such that the heritability was high in high-SES families, but much lower in low-SES families.