What does "tip of iceberg" mean? Is it an idiom?

Native speaker’s answer
Rebecca
Yes, "tip of the iceberg" is an idiomatic expression. Usually when you see part of an iceberg floating above the water, that part which is visible is only a very small portion of the much bigger whole floating below the surface. Thus, this expression is used to say that something is only a small part of an issue or problem that is much bigger. It's usually used in negative contexts, although this is not the case for this video. Ex: Flunking my math class was only the tip of the iceberg. Ex: We found out that the ripped up sofa was only the tip of the iceberg. Our dog destroyed the house while we were gone.