This digest-sized book contains a seemingly random collection of words, phrases, and strange mnemonic aids. Three times each day, a bard can consult it while using the lore master class feature in order to gain a +5 competence bonus when taking 10 or taking 20 on a Knowledge check.
Loremasters have a class feature that is effectively the same as bardic knowledge and are rather booky folk. But the text seems to exclude anyone but bards from using this book.