A commonplace book (from Latin locus communis, in turn from Greek tópos koinós) is 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). 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.
(Compare to R. Buckminster Fuller's chronofiles, which consist of a time-series record of his life from 1920 through to 1983.)
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.