When someone shares one of your pages or posts on social media an image can be included. Each of the social media sites use a different size image with the share. You can specify the image used via background coding of your site.
As mentioned above each site uses a different size. Not only that, they keep on changing them.
If you find a current
list of sizes please post them here.
I'll start with this list which includes:
Infographic: Social Media Image Size Guide (2020 Edition)
23 June, 2020