There are different types of copy editing including content editing or line editing and developmental editing. Line editing is the predominant service I provide. This involves reviewing a manuscript line by line (appropriately named, huh?) and ensuring that there are no misspellings, mechanical errors, plot holes, etc.
What does copy editing mean? The Chicago Manual of Style defines copy editing as, “the process of reading a text and scrutinizing all its components to find errors and mark them for correction." Here is a list of what I would be doing:
Mechanical editing: Ensure consistency in all mechanical matters—spelling, capitalization, punctuation, hyphenation, abbreviations, format of lists, etc.
Correlating parts: Check contents page against chapters; check numbering of footnotes or endnotes, table, and figures. Check alphabetization of bibliography or reference list; read footnote, endnote, or in-text citations against bibliography or reference list.
Language editing: Correct all errors in grammar, syntax, and usage. Point out or revise any contradictory content. Point out any patches that seem wordy or convoluted, and supply suggested revisions. Ask for or supply definitions of terms likely to be new to readers.
Content editing: Query any facts that seem incorrect. Use desktop reference books or the Internet to verify content. Query faulty organization and gaps in logic.
List adapted from Amy Einsohn's The Copyeditor's Handbook