Incredibly means to such a great degree that it's hard to believe. When something is incredibly difficult, it's so challenging that you might wonder if anyone could do it. When a roller coaster is incredibly fast, its speed amazes you.

If your friend tells you she saw an incredibly huge dog, she means it was so enormous that you'd struggle to imagine it until you saw it yourself. When scientists discover an incredibly old fossil, they mean it's so ancient that the number of years is almost impossible to comprehend.

Notice that incredibly doesn't mean something is actually unbelievable or false. It's a way of emphasizing just how extreme or remarkable something is. A math problem might be incredibly complicated, a gymnast might be incredibly flexible, or a book might be incredibly boring. The word intensifies whatever comes after it, showing that something goes far beyond ordinary or expected levels.

People can overuse incredibly when they just mean “very.”