What makes someone a 'good singer'?

I wasn't sure of where else to post this, so I thought I'd ask here; in your opinion, or based on your experience, what makes someone a good singer? What must they do or not do in order to be called that?

I've been told I'm a good singer/can sing well by people close to me, but I have just been telling myself that their opinion is biased, so this would help me too.