For me, a friendship is based on two people who genuinely enjoy each other's personality and company. I've got some friends with whom I'll talk on the phone, and the next thing I know, three hours have gone by.
The lady who lives next door to me is like that. Her husband is a great guy but I have more in common with her. We're the same age, grew up in the same area, went to different high schools, but graduated the same year. We even discovered we were born in the same hospital, and yet I never met her until they moved next door last year. I have to be careful when drinking with her, because I'm likely to polish off an entire bottle of rum or vodka, stumble back home and retch in the grass along the way.
I have another friend whom I've known since the age of five. I don't see him so much any more but he's not that far away, and when we do get together, it's like we always pick up where we left off last time.
The guy with whom I work most closely is ten years older than me, and he's become like a brother to me. He and his wife had Thanksgiving dinner with my wife and I, along with my brothers and sister.
Of course, I have friends I see every year at NEST...friends whom I think it would be really cool to see more often, but distance comes into play.
I don't know what qualities it is that make me regard people as friends, other than I like them and they like me. Maybe that's all we need.