last volume; second volume (of two); third volume (of three)
Refers to the final volume in a set of two or three. In a two-volume set, it is the second; in a three-volume set, it is the third. Often contrasted with 上巻 (first volume) and 中巻 (middle volume).
The last volume of this novel will be released next month.
I ended up reading only the second volume of the two-volume set first.
first and second volume; two-volume set
Compound of 下 (げ, 'lower, last') and 巻 (かん, 'volume, scroll'). The reading げかん is the on'yomi of both characters.