https://srhd.org/news/2021/coronavirus-mutations-and-variants-what-does-it-mean#:~:text=We%20know%20the%20coronavirus%20curre ntly,strains%20and%20almost%204000%20variants.
Organisms in general, be it humans, plants, insects, bacteria, or viruses, undergo genetic mutations which can be beneficial or detrimental. Although viruses are not technically alive, these also mutate and evolve as they infect a host’s cell, replicate and move on to another cell or a new host. The process by which a virus spreads is what we call transmission. There are differences in the rates of mutations amongst different types of viruses. As an example, the SARS-CoV-2 coronavirus which causes the clinical entity we know as COVID-19 mutates approximately every 11-15 days. That is about half of the rate of influenza (flu) and about a quarter of the HIV rates. Mutations generate variability within a population, which allows natural selection to amplify traits that are beneficial, in this case, to the viral particle, as viruses are not considered organisms per-se.
We know the coronavirus currently has 12,700 identified mutations, 12 main types of the virus (identified as 19 A, the original type, through 20 J), five strains and almost 4000 variants. The strains are known as L, the original strain, which mutated into the S strain followed by V and G (further mutating into GR, GH and GV, and several infrequent mutations collectively grouped together as O). The G strains are now the dominant strain around the world. SARS-CoV-2 variants with spike (S)-protein D614G mutations have become the most common variant. It is so named because one amino acid is changed from a D (aspartate) to a G (glycine) at position number 614 of the viral spike proteins.