to skim means speed reading, or reading quickly, or using various faster techniques to learn new materials while reading.
When someone is “skimming” it means they read only the headlines, or only the conclusions, or only looks at the pictures, or only looks at summaries. They want to get the “main ideas” but know they will not get all of the details.
So I call myself a “skimmer” because that is how I read difficult books. I am restless and impatient but by setting targets while reading such as: absorb an overview of a book as quickly as possible and find what is interesting to me to focus further on, then I have an easier time working with a difficult book.
Since academic books such as this book usually follow patterns such as:
they always have introductory paragraphs at the beginning of chapters
they always have concluding paragraphs at the end of chapters, It becomes possible to “skim a book” that is organized like this quickly by learning its rules.