Assalamu Alaikum and Welcome to Salam World!
"Salam" - Islamic Greeting of Peace - Muslims all over the world use the Islamic form of greeting, "Assalamu alaikum", which means peace be upon you. When two Muslims meet who are total strangers to each other, the moment they use this greeting, they immediately feel that they have common grounds, even when they do not speak each other's languages. The Islamic greeting has its different versions, the shortest of which is the one we've already mentioned. The rule in Islam is that when we are offered a greeting, we return it with a better one, or with its equal at least. God orders in the Qur'an:
"When you are greeted with a greeting, greet in return with what is better than it, or (at least) return it equally. Allah is Ever a Careful Account of all things." [Surah An-Nisa'; 4: 86]