Is it illegal to share GOG games?

Hello there, I'm curious about something related to digital gaming. I've heard of GOG games being shared among users, but I'm not entirely sure if this practice is within the legal bounds. Can you clarify for me? Is it actually illegal to share GOG games with others, or are there certain conditions under which it's permissible? I'd appreciate any insights you can provide on this matter. Thank you in advance!