That an interesting and complicated question. Many think it is any other nation then the one they live in. While correct it is not the full answer. When someone becomes a “Christian” we are instructed within the Bible to separate ourselves from the world yet to still be a part of it. Why? So we can be an example to all others within the world of what believing in Jesus Christ as the Son of God really means. So the real answer to that question is anything around you is the “world.” That includes what and who you invite into your home. “Why that wording of the sentence?” you ask.
Every television, radio and computer is an entrance into your home. What you place upon the screen or station is something from the world in most cases. Due to computers most cable companies and networks know how popular a show is, which constitutes them continuing to produce them. I actually have several channels blocked on my TV because I feel they do not promote what I feel is the correct message for my family to see or hear. I will not bother telling you which one, but I will tell you that it boils down to what is taught within the Bible. I do not care how “wholesome” a show may appear if it has elements that are not seen as correct within the Bible it is not allowed. Now if enough people followed this practice you would see how shows start to change for the better. This is just a little example, so I will expand into what is the “world.”
The world is everything outside your home as well. Again your actions and behavior are themselves a witness to God if you call yourself a “Christian,” yet many that do call themselves this live their life’s like they are of the world. Well here is some news for you. It is because they are of the world. People live what they truly believe. If they truly followed God they would do things like vote, write their government representative, help those in need; talk to those that sin and help them understand that their life is not on the right track to an eternal life in all of God’s creation.
In reality extremely few do this. My statement to this is that “few” are the real “Christians” for they are living what they believe and ARE being a shining light of God unto the world about them. If any calls themselves “Christian” this is what we are told and taught we must do. We must through our deeds, action and words be a shining light unto the world about us daily. Showing that through our life choices that there really is something called a “God” and His Son is the Lord our Savior Jesus Christ.