"Friend" is a strong word for me. For one, I don't really consider someone my friend until we talk on a frequent and mutual basis. If I'm the only one ever making the effort to communicate, I'll eventually just drop the person. If we don't have enough to talk about to keep things from getting dull every time we interact, or the other person doesn't show interest in talking outside of brief exchanges when we happen to cross paths, then they're just an acquaintance. I can be on good terms with people and not consider them part of my friend circle.

My friends are the ones who seek to actually stay in touch outside of the context in which we met. We exchange contact info, talk about more than just one subject, are at least somewhat comfortable enough to discuss serious or personal things and open up to each other (of course the degree of this will vary). We have things in common, share things we think the other would be interested in, and care about each other beyond meaningless things like memes and small talk. That's the bare minimum for me.