I found some people call others 老铁. What does this mean? Does it mean friend? I can't find this usage in any dictionaries.
According to baidu
Which also fits with the use of it as far as I have seen it
老: literally means old, but by adding in front of a pronoun, it produces a sense of intimacy.
老王 (Mr. Wang, but most likely someone you are famaliar with)
铁: literally "iron", describes a strong relationship.
铁哥们 (buddy, has a stronger relationship than "老哥")
巴铁 (some Chinese use this term to describe the relationship between China and Pakistan (巴基斯坦))
Note: The word is an internet slang derived from Dongbei dialect, so of course you can't find any definition in a formal dictionary.