いらっしゃい  irasshai

いらっしゃい  irassha...

いらっしゃい

When you enter a restaurant, people usually say いらっしゃいませ。
It is a polite way of saying いらっしゃい。

It means welcome!!!

This is different from どういたしまして dou itashimashite ... means "You are welcome." or "Don't even mention it."