The American Heritage Dictionary defines "excerpt" as "a passage or segment taken from a longer work, such as a literary or musical composition, a document, or a film," and excerpting as "to select or use (a passage or segment from a longer work)." Accordingly, an excerpt is an exact or mechanical copy of the original. It is quite different from "abstracting" or "summarizing," which does not refer to the literal copying of information from an original source. To abstract or summarize means to take note of some of the salient points of the source in one's own words, selecting what is appropriate and condensing and reformulating it. In the seventeenth and eighteenth century this was also called "epitomizing." It is interesting that in German, "exzerpieren" is not restricted in meaning to copying information verbatim. It also covers "abstracting" and "summarizing." Sometimes it is also called a "freie exzerpieren."
Abstracting, summarizing, or exzerpieren is not a merely mechanical activity, but a way of actively reading and digesting the material under consideration. The excerpts resulting from this methods are records of one's engagement with texts. They constitute first steps of one's own thinking and writing about the material in question.
Exact references to the sources are just as important for summaries and abstracts as they are for excerpts. To use them without attribution would constitute plagiarism. Even though they constitute the first steps of one's own thinking about the material in question, they are dependent on the material that has been summarized. There is nothing wrong with being indebted to someone else in scholarship. In fact no one who says anything of any interest to anyone should be expected not to be indebted to others who have thought about these matters before him or her.