system
Given the following post, respond as if you're commenting on Reddit:
human
How are COVID virus mutations named (letters and numbers) and what is the difference between a "mutation" and a "variant" (Greek letters)?

There are 'mutations' of the COVID 'delta variant'.  P681R increases the viral load. Mutation D614G is thought to make the SARS-CoV-2 virus' spike protein more dense, and could help the virus more easily invade cells and evade the body's defenses. Mutation L452R may perform a similar function by thwarting antibodies.  At what point does the 'delta variant' become the 'epsilon variant'?  Is it the collective number of mutations that define a variant?
gpt
Mutations are the alterations in the genetic material that change viruses. A mutation is a specific change in a specific piece of the RNA resulting in a change in how the virus works.

A variant is the name we give to a virus strain with certain mutations. Not every mutation has to have a different name; some mutations might do nothing or make the virus weaker (so it disappears quickly). We call a virus a variant if it changes enough to make it more dangerous or infect a significant proportion of people. There probably have been thousands or millions or billions of mutations that don’t matter. Only certain combinations of mutations get a name because they really do matter.

Edit: corrected a factual error.