I was reading an article lately and encountered this, "Reviewing all the data, Andersen et al. have concluded that the natural selection of the virus could have happened in animals, before zoonotic transmission, or in humans, after zoonotic transmission." So, I was wondering, what is the meaning of "the natural selection of the virus"?
Natural selection has a single meaning whether in the context of viruses or anything else. I think you should read the whole explanation, but it boils down to this: 1) organisms randomly mutate; 2) useful mutations are selected for better fitness and kept in the population.
I think it is great that you are reading so many articles. Still, I don't think this forum is meant for answering so many questions of the type
what is the meaning ...?, especially when they are easy to answer by Googling and when they are unrelated to bioinformatics.