Heritability is a measure of how much of the differences between people on a given characteristic can be attributed to genetics. More specifically, it is an estimate of the amount of variation between individuals in a given population that can be accounted for by genetic differences. Behavioral genetics research indicates that every trait is (at least) a little bit heritable—though the fact that a trait is heritable does not mean it is fixed.
Heritability estimates range from 0 to 1, or from zero percent to 100 percent. For example, if the heritability of a trait is estimated to be 50 percent, that suggests that about half of the overall variation between different people on measures of that trait—within the specific group of people measured—is due to differences in their DNA. (If heritability of a trait was 100 percent, identical twins, who share the same genetic code, would be exactly the same on that trait—but that doesn’t actually happen.)