i have to say that's a very good question.cause I think a lot of people in China maybe don't know what it is.it's very simple.which means "Iron wrapped in meat"for example,you ride a bicycle or motorcycle.and"you（你）"means"meat（肉）","bicycle or motorcycle（自行车或者摩托车）"means"iron（铁）".as we all know bicycles are made of iron,that's“肉包铁”. there is another word called“铁包肉”，for example,you take a train or a plane.this vehicle is wrapped around you,that's“铁包肉”. and last,im sorry to use my embarrassing chinglish to explain it for you.I'm very happy to help you!