In Italian, "ei" doesn't have a specific meaning as a standalone word. It is possible that people are using "ei" as a colloquial way of addressing someone, similar to the English informal greeting "hey" or "hi." It's more of an informal way to get someone's attention or start a conversation, especially among friends or acquaintances.
In Italian, there are various informal greetings or interjections used in different regions or social groups, and "ei" might be one of them. Keep in mind that the use of such greetings can vary based on context and the relationship between speakers. If you are uncertain about the meaning or usage of a specific term or phrase in Italian, it's always a good idea to ask the person who used it for clarification.