One word can be referred as many other words like a Green Beret can also be referred as Military, The Green Beret book by Robin Moore, The Green Berets movie about the American Vietnam War etc. this way people come up with their own slang language with people you are in a friendship term, kind of like a code language that they could speak without people being completely clueless what they are talking about. Another advantage of colloquial terms is you can make the most filthy, annoying, offending word into something sweet and cute atleast not more than the actual word used for it or may be so cute that people take an insult as a compliment. No wonder people curse a lot these days in their own slang language. In the same way multiple colloquial terms are being used for friendship defining a huge sentence in jus one or two words.
Some of the colloquial terms used for the friendship terms are true friend meaning friends who are truly there for you when you need them, fair-weather friend meaning a friend who only supports you when things are going god and easy for you, casual friends meaning those friends who have causal sex often but are not really committed neither they keep their relationship till just being friends. Some people often refer to this kind of friendship as friends with benefits. A best friend that we are all familiar with is probably the one used far more often. It means that two people, who are in on everything together, give company to each other and people will always see them together talking, laughing, busy in their own little world. Best friend forever is another friendship term meaning friends who will stay friends forever although usually this kind of friendship mostly ends up in a fight. Another sophisticated word used to express a friendship term is acquaintances which is usually used in blogs, forums etc but hardly by people.
Some might jus use buddy, best buds, best buddy, best pal and soul etc to express their friendly relationship with another. This is more of a casual and cool way to express a friendship term. A hoss is a Southern colloquial nickname for a partner or a friend. Some people also use the phrase “just friends” meaning that people might think they are involved or they might have gone out in the past but now they are keeping their relationship to just staying friends where no sex or flirting is implicated.
These friendship terms are widely and commonly used by any teenager, internet friends to let the other person know what they really think or feel about them. This way a small word of friendship has been further divided into other kinds of friendship. Apart from these friendship terms people have come up with a number of colloquial terms for different words to give more meaning and depth to the language this can either be in English or any other language.