Q: Context: "Survival of the fittest" is a phrase that originated from Darwinian evolutionary theory as a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success. In Darwinian terms the phrase is best understood as "Survival of the form that will leave the most copies of itself in successive generations."

Question: what is meant by the phrase survival of the fittest?
Let's give stream of consciousness below
The relevant sentence in the passage is: "Survival of the fittest" is a phrase that originated from Darwinian evolutionary theory as a way of describing the mechanism of natural selection. So the answer is way of describing the mechanism of natural selection.