noun
marginal notes; glosses
Refers to notes, comments, or glosses written in the margins of a text.
古文書の余白注を読むと、当時の読者の考えがわかる。
Reading the marginal notes in old documents reveals the thoughts of readers at the time.
欄外注 also means marginal notes, but 余白注 emphasizes the blank space (余白) itself.
Compound of 余白 (margin, blank space) and 注 (note, annotation).