As used in this chapter, unless the context otherwise requires:
 1. “Book”, “list”, “record”, or “schedule” kept by a county auditor, assessor, treasurer, recorder, sheriff, or other county officer means the county system as defined in section 445.1.
 2.  “Mineral interest in coal” means an interest created by an instrument which creates or transfers either by grant, assignment, reservation, or otherwise, an interest of any kind in coal, as described in chapter 207, without limitation on the manner of mining the coal.