Com - mon - place Book
a book into which notable extracts from other works are copied for personal use.
Commonplace books (or commonplaces) were a way to compile knowledge, usually by writing information into books. Such books were essentiallyscrapbooks filled with items of every kind: medical recipes, quotes, letters, poems, tables of weights and measures, proverbs, prayers, legal formulas. Commonplaces were used by readers, writers, students, and scholars as an aid for remembering useful concepts or facts they had learned. Each commonplace book was unique to its creator's particular interests. They became significant in Early Modern Europe.
"Commonplace" is a translation of the Latin term locus communis (from Greek tópos koinós, see literary topos) which means "a theme or argument of general application", such as a statement of proverbial wisdom. In this original sense, commonplace books were collections of such sayings, such asJohn Milton's commonplace book. Scholars have expanded this usage to include any manuscript that collects material along a common theme by an individual.
Commonplace books are not diaries nor travelogues, with which they can be contrasted: English Enlightenment philosopher John Locke wrote the 1706 book A New Method of a Common Place Book, "in which techniques for entering proverbs, quotations, ideas, speeches were formulated. Locke gave specific advice on how to arrange material by subject and category, using such key topics as love, politics, or religion. Commonplace books, it must be stressed, are not journals, which are chronological and introspective." 
Source : Wikipedia