Many people can give a single good performance. Even non-actors.
But in my book, a really good actor has the following:
Believability (convincing in their work)
Versatility (able to embody a variety of characters)
Longevity (sustaining a quality of excellence over a career, not just an isolated instance)
Reliability (can be counted on to bring something wonderful and memorable to their work)
The list of people who have demonstrated "good acting" is a lot larger than the list of people who I would call "good actors."
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22