Natural selection is the process by which individuals with characteristics that are advantageous for reproduction in a specific environment leave more offspring in the next generation, thereby increasing the proportion of their genes in the population gene pool over time. Natural selection is the principal mechanism of evolutionary change, and is the most important idea in all biology. Natural selection, the unifying concept of life, was first proposed by Charles Darwin, and represents his single greatest contribution to science.

Those traits which helps to survive the organism due to more favourable variation then others.
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations.
Sorry in simple way it is the key of evolution
The process by which the animals and plants suit to the condition in which the y live more longer than other
Selection of traits by nature

The selection done by nature for eg. There are two types of beetles in a pond one is red and second is green , the beetle which adapt the region and environment will selected and other will definitely die

In simple words (Survival of fittest).Nature select those who r fittest in all to survive on the earth.Rest gets rejected and die.

It means that the nature select the best one who os capable to survive in that habitat

The selection done by nature for its survival
All organisms of specific variation selected by nature and else all are destroyed then it is a natural selection