What is a compounding fracture?

Hi folks,

I have a question which is plaguing my mind. I went into my
family doctor after a series of x-rays, and he has informed
me that I have a compounding fracture in one of the
vertibrae in my lower back. He told me it was serious, but
was an hour behind schedule and did not offer me much
explanation on what this means.

My logic justifies that the fracture which is continuing to
'crack' under the weight of my torso. The injury is now two
months old. I was hoping somebody might be able to give me a
slightly detailed, yet still understandable explanation of
that this means is happening in my body.

-Evan