Quite possible the greatest friend you'll ever have, so good, in fact, that there isn't a word good enough to describe it so you use the word acquaintance.
A person you slightly know about, but they aren’t your closest best friend or a stranger you know absolutely nothing about.
For example, you may know the old man at the grocery store you go to often is named Bob and he shows up the same days as you, and you guys say hello to each other time to time, but you guys aren’t best friends or strangers. That would be an example of an acquaintance.
The act of, after being (re)introduced to a person of former/new acquaintance, maintaining a tie via text, phone, etc in the event something more could come of the (re)introduction; such as friendship, sex, love, etc
Oh, I knew of Bob in high school, and I had a chance to get to know him a little at the 10 year high school reunion. I really like him. He was my best friends brother's best friend! Too bad we live in different states. Looks like I'm going to have to do some "acquaintance maintenance" to see what comes of this!
A "secret code" phrase to mean that --- while you are not of alternative orientation yourself --- you are at least "neutral and tolerant" in your views/feelings regarding other-than-straight individuals, and so anyone within earshot knows that he can feel comfy and secure around you, no matter what type of human he identifies himself as.
Jerry Dean Michael (a.k.a., "Elizabeth Carmichael", the infamous proponent of the equally-infamous "Dale" automobile) might have been able to label himself as a "friend of Dorothy" back in the beginning, but after he swindled so many people out of their life savings in their eager bids to acquire one of his non-existent fuel-miser automobiles, he could probably only have claimed to be an "acquaintance of Dorothy", since neither the Kansas girl or anyone else would likely have wanted to be HIS "friend" anymore!