Commonplace books (or commonplaces) are a way to compile knowledge, usually by writing information into books. (And on a computer or in a blog) Such (paper) books were essentially scrapbooks 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.
I do write a (paper) commonplace book. And blogging to me is commonplacing too.