It's what happens when you make a union of an int and a float and write it as an int and read it as a float.
Most compilers will do something like "treat the bits like they represent a float, even though they mean something else when they're treated as an int."
But the language spec says the compiler is allowed to send an email to Bjarne Stroustrup with your home address so he can come over and personally set your computer on fire.
