Commonplace books (from Latin locus communis, in turn from Greek tópos koinós) are a personal repository of thoughts, knowledge and insight; they are essentially scrapbooks filled with information of every kind (recipes, quotes, letters, poems, tables of weights and measures, proverbs, prayers, legal formulas – Wikipedia). Each is unique to its creator’s particular interests, and may be organised and cross-referenced in various ways. They became significant in Early Modern Europe.
In a lot of ways, this lexicon is my commonplace book. I should probably put more effort into it, as always, but I’m just one man.