1)When something is translated into another language, and sometimes translated back into the original language, and because of differences of the languages some of the original meaning is lost.
2)Whenever someone re-does something in a new medium (for instance, a movie based on a book) and, due to differances between the mediums, some details and the original meaning is not present.
3)A movie that came out in 2003.
1)See larstait's post for a good example.
2)"Did you like the new Harry Potter movie?" asked Maria. "No," answered Sharon. "They couldn't include all the details that were in the book because then the movie would be too long. A lot of the characterization and subext was lost in translation."
3)I really liked Lost in Translation. And if you didn't, your opinion can't possibly be worth anything, you must be an idiot or a philistine. No, I didn't just imagine the subtext, it's there and it's very moving!