A more thorough explanation:

NONSTATUTORY SUBJECT MATTER

Nonstatutory subject matter refers to things that cannot be patented because they do not fit into any of the categories of things that are legally patentable. Examples of nonstatutory subject matter include works of nature, abstract ideas, and human movements.

• A rock formation that occurs naturally in a national park
• An idea for a new way to organize files on a computer
• A dance routine performed by a professional dancer

These examples illustrate nonstatutory subject matter because they cannot be patented. The rock formation is a work of nature, the idea for organizing files is an abstract idea, and the dance routine is a human movement. None of these things fit into the categories of things that can be legally patented.