An iceberg is a big chunk of ice that breaks off from a glacier or ice shelf and floats in the ocean.
When we talk about an iceberg, we often think of it as just the small part that's visible above water. But what's really interesting is that most of the time, the huge majority of the iceberg is hidden underwater - maybe 9 out of 10 parts! So when something seems big and impressive on the surface but there's much more going on beneath, we say "it's like an iceberg" or "there's an iceberg effect." It means you can't see everything at first glance.
A huge mass of ocean-floating ice which has broken off a glacier or ice shelf
Example: The Titanic hit an iceberg and sank.
