Heidegger's Bible Handbook: Ruth: Title and Canonical Position
1. Ruth is an appendix to Judges. The name of the book. It is the Second of the Megilloth.
The Book of Ruth is to a certain extent an appendix to the Book of Judges. For, what things are narrated in it, happened בִּימֵי הַשֹּׁפְטִים, in the days of the Judges (Ruth 1:1). And the book is called רוּת/Ruth, ἐπειδὰν καὶ τὴν περὶ τῆς Ροὺθ ἱστορίαν μόνην περιέχει, because it comprehends only the history of Ruth, says Saint Athanasius in his Synopsi. The Hebrews put it in a second place among the חמשׁ מגלות, Hamesh Megilloth, the Five Little Books (Song of Solomon, Ruth, Lamentations, Ecclesiastes, and Esther), so called κατ᾽ ἐξοχὴν, par excellence, by them, and wont to be read throughout the year at the feasts.