What one defines as good can be different from person to person. What I broadly define it as is in terms of tabletop alignment, good is putting the good of others when you could just be selfish. A good aligned person looks sees how they may help someone else, and either rejects or not even thinks how they could benefit, they are motivated by how they can help others.
But whether they are aligned good does put some question in whether they are contextually good. Someone who cares about others over themselves can do some bad things, like a bible thumper could tell atheists they are going to hell, one might be confused that conversion therapy is something helpful, one might even be so confused that they think killing people is helping their souls. By the same vein, someone who does charitable things that help others may not actually be a good person, they could be obsessed with making themselves look really kind and helpful as to gain social clout, while actually not caring if it really helps others.
Putting aside ulterior motives, I think the only way you can know someone is good is if they genuinely care about whether someone helps others, and in context I would say they try hard enough question if what they are doing is actually right. Not to sound anti-religion, but I think the important part of that is fighting against what might feel familiar and comforting, as beliefs can blind you from what actual good you are doing. Fighting against your own ignorance and not trusting in ancient texts.
In the scheme of things, I bet I don't live up to other people's ideas of being good, like I don't go around saying hi to people. My reason being my social anxiety makes me terrified of being a nuisance to others, so often avoiding people is my way of trying to not inconvenience others. I otherwise may hold doors open for others, hate lying or any perception of taking advantage of something I don't deserve. When I play a video game, I can't stand the idea that I do a bad and terrible thing to someone else, even though I know that they are fictional characters, I feel too bad when I could have solved things in a peaceful way, that does not cause further harm.
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Through dream I travel, at lantern's call
To consume the flames of a kingdom's fall