What it means to be "White"

In my critical perspectives course, one of the texts were reading deals with multicultural education. In the book, the author talks about that though the dominate culture in America is white, “White” people don’t have a sense of culture or identify. In other words, if you asked me what I identified with, I might say “American” but I couldn’t tell you what the definition of being “American” means. And if there was an “American” culture, what are some of those characteristics?