To me, "friend" and "close friend" are synonymous. To be my friend is a very difficult thing to achieve, because I don't consider casual people who just "hang out" to be friends. That is an acquaintance.
A friend is someone who is very close to me, someone I trust completely, and someone, most importantly... who spends A LOT of time with me. Talking constantly in any way. Whether on the phone, over the internet, etc. We talk about all sorts of things, we divulge and know a lot about each other. And it is mutual. It has to be mutual. It doesn't matter what we do, as long as we share our sorrows, our happies, and all kinds of things with each other. To me, talking is an important foundation of a friendship. Because it's been the only foundation of most of my friendships. (As I haven't had many real life ones)
An acquaintance is a person who I am vaguely friendly towards and is also friendly towards me. But I have no attachment to them, nor they to me. I do not care very much about them, except for some brief entertainment and spending some little bits of time together. I don't tell them anything beyond the very basic.
To prove yourself worthy of being my friend, passing from acquaintance into that... well, you have to show me that you can put up with the real me. Not the me I put on to acquaintances where I keep everything a secret. The me who is often emotionally unstable, and gets randomly depressed out of nowhere. The me who often doesn't feel well, the me who has a lot of needs in a friendship, the me who is creative and wants to ramble about the things I just made. You have to handle that, and maybe even enjoy the positive creative aspects of me. Having a lot in common helps, as does having a lot to talk about. And you have to just "click" in this way I can't explain. It takes certain types of personalities to be compatible for me with a friendship. I'm not even entirely sure what they are. There just has to be some special bond between us. Some great way we work together as well, because it isn't just about me. We have to be a team. And I have to realize and consciously acknowledge that it exists. Because most of the time, I am so distant from other people due to fear of getting abandoned and hurt yet again that I have to actively say to myself: "This person... they really are that important to me. We love each other." To break past the initial coldness.
It doesn't matter how long I've known someone for this to happen. What matters is how long we've spoken. If we only spoke once every six months, it wouldn't matter if I knew them for ten years. Conversely, if I know someone for only one year, but we spoke almost every day of that year... well, I think that counts a lot more. They would probably be someone I would divulge a lot of my secrets to. The person has to prove that they're invested in this relationship, and willing to make time for me. That they actually give a crap about us talking and spending time together.
Friendships can be romantic or not. I don't really care. I don't distinguish. For instance, my fiance is currently the best friend I've ever had. Our relationship is based on our strong friendship. A friendship based on three years of talking everyday.
Also, due to my strange definitions of friendships, there have been a lot of people in the past who just consider me a friend when I don't. And it makes me feel awkward and uncomfortable. I often humor them just to avoid hurt feelings. For instance, I had someone I knew for many years. But I felt no particularly close attachment or caring of them. They considered me one of their best friends, but I did not consider them the same due to the fact that most of our conversations were about them and their problems. It was too unbalanced for me to feel invested and I felt they didn't really know me at all. Whenever I tried to talk about myself, the conversation would go silent. Of course, nowadays, I just pretty much don't even bother with such one-sided pursuits.