The hollowed-out impression formed when the original parts of an organism in a sedimentary rock are weathered and eroded is called a mold.

Here's why:

* Mold: This is the negative imprint of the original organism. Think of it like a footprint in the sand. The organism is gone, but the shape it left behind remains.

* Cast: If the mold later gets filled with sediment that hardens, it creates a positive replica of the organism called a cast.

So, the process goes like this:

1. Original organism: A shell, bone, or other part of an organism is buried in sediment.

2. Weathering and Erosion: Over time, the original part of the organism is broken down and removed.

3. Mold: The space left behind by the organism is the mold, a hollowed-out impression.

4. Cast (optional): If sediment fills the mold and hardens, a cast is formed, a solid replica of the organism.