> It’s hard to define exactly what a “classic game” is, but for the sake of this study, we looked at all games released before 2010, which is roughly the year when digital game distribution started to take off.

https://gamehistory.org/study-explainer/

From the excecutive summary of the original study:

They analysed a dataset of ~4,000 video games released in the US before 2010.

https://zenodo.org/record/7996492

I'd say it's a video game of outstanding merit relative to other video games of its time.