Tata 0487 is absolutly right ! If you say "hola", when you find someone you know in a street, generally it means that you're at least willing to make a little stop and chat a little, you know, "a long time without seeing you", ect. But when you don't have that time to spend, you smile and say "adios", but you NEVER stop...you must keep going on. If you stop and you say "adios" you look crazy...Imagine if you stood in front of a friend and say "Gooby"...weird! The only languaje I know in which you use the same word for "hello" and "goobye" is Italian, with the "ciao" word....

When you meet some person on the street you can either say "hola" (hello) or "adios"/"chau" (bye but here meaning something like 'see you'). If you say "hola" you're meaning to have some kind of conversation at least a little, but if you say "adios", as tata said, you're not interested or not have time to have a talk. I personally use "chau" for close friends or young people and "adios" to adress elderly or show someone more respect.

well, is a weird way to say hello, but you use it when you have a rush, and you don't have time to make a little chat. It's like I don't have enough time for you so I don't say hi, I just say goodbye and that's it.

You can also avoid a confusion saying "Hola y adios" or "Hola y hastaluego" or "Hola y chao" Or just "Adios" but be careful never say just "Adios" if you casually see your boss or somebody important, you must be more polite about the word "chau" or "chao" (we say "chao" in Colombia, not "chau") and "hola" they're like the words "hi" or "see you", that is, to be used with close people i guess "chao" came from italian word "ciao" but in spanish it's just for when you leave, not to say hello

adios = adieu = I am not going to see you in a long period of time or you dont want to talk with the other person. bye