I have been trying to find a good and simple definition of the term " genetic load". I have found several, of which the most simple said something like " the number of lethal genes carried by an average individual of the species".

The majority of other definitions were phrased in such a way, that I usually lost the meaning halfway to the end.

Genetic load is the reduction in selective value for a population compared to what the population would have if all individuals had the most favored genotype.[3] It is normally stated in terms of fitness as the reduction in the mean fitness for a population compared to the maximum fitness.

Genetic load is a number between 0 and 1 and it measures the extent to which the average individual in a population is inferior to the best possible kind of individual. The genetic load equals the relative chance that an average individual will die before reproducing because of the deleterious genes that it possesses. Ignoring frequency-dependent selection, it is calculated as follows:

Suppose there are a variety of genotypes in the population, each with its characteristic fitness; one genotype has a higher fitness than the rest and we call its fitness Wopt. We can also measure the average fitness of the whole population; it is just the fitness of each genotype multiplied by its frequency: it is called mean fitness and is symbolised by v.

What is correct?