It refers to the books such as "Noin Utamakura," a Kagakusho (a book on the study of waka poems) explaining utamakura, and "Utamakura Nayose," a list of utamakura.
歌枕の解説が書かれた歌学書の『能因歌枕（のういんうたまくら）』や一覧を列記した『歌枕名寄（うたまくらなよせ）』などの書物のこと。