Word for a book or notebook that describes the contents of a specific set of other (note)books

I'm uncertain about any technical term but I believe they are referred to as indices (sing, index) or content books. (Notebook of contents may work but that seems and sounds silly.)

I have a full set of printed encyclopedias from the 1960s and it includes exactly such a volume, which consists of an overview by theme with many cross-references, followed by a normal index with keywords and page numbers. The title of this volume is Index and Guide. Hope that helps.

Propaedia

Wikipedia says this>

The one-volume Propædia is the first of three parts of the 15th edition of Encyclopædia Britannica, the other two being the 12-volume Micropædia and the 17-volume Macropædia. The Propædia is intended as a topical organization of the Britannica's contents, complementary to the alphabetical organization of the other two parts. Introduced in 1974 with the 15th edition, the Propædia and Micropædia were intended to replace the Index of the 14th edition; however, after widespread criticism, the Britannica restored the Index as a two-volume set in 1985. The core of the Propædia is its Outline of Knowledge, which seeks to provide a logical framework for all human knowledge; however, the Propædia also has several appendices listing the staff members, advisors and contributors to all three parts of the Britannica.

Since metadata is

data that provides information about other data. [M-W]

, perhaps you could coin the term meta-notebook !