make a world a difference 大不相同、是两码事
e.g. There's a world of difference between liking someone and loving them（说一个人，但没有明确男女，可以说they/them/their ...）.
what a small world! 世界真小（意外遇见某人）
e.g. What a small world! This is our third time meeting each other in two days!
mean the world 意义重大
e.g. Winning that contest meant the world to me. All of my hard work finally paid off（成功、奏效、达到目的）.
it's not the end of the world 这不是世界末日、还有机会
e.g. Come on, hang in there（挺住、撑住、坚持住）! It's not the end of the world!
think the world of sb 对某人评价很高
e.g. My dad thinks the world of you. I believe he wants you to be his son-in-law.
on top of the world 超级开心
e.g. I was on top of the world when my mom told me that we were going to Paris on vacation.
out of this world 非常好的
e.g. The meal was out of this world!
see the world 见多识广、见世面
e.g. You're young and you have to see the world.
the world over 全世界、世界各地
e.g. People are basically the same the world over.