which of the following words best matches this definition: The process in which the best adapted organisms survive and pass on their traits, while those that are NOT well adapted do not survive.

Survival of the fittest

Explanation:

According to the Darwin's theory of survival, a species can survive among its peers only when it is fit enough to adapt to the natural changes and hence remain alive till its reproductive stage in order to produce fertile offspring.

Such species which survive are known as fit species while the remaining unable to cope with changing environment die out at an early stage of life.