first and second volume; two-volume set
Refers to a work published in two physical or digital volumes, typically labeled 上巻 (first/upper volume) and 下巻 (second/lower volume).
This novel is divided into two volumes.
You get a discount if you buy the two-volume set.
Means 'all volumes' or 'complete set', used for works with any number of volumes, not limited to two.
Compound of 上 (じょう, 'upper/first'), 下 (げ, 'lower/second'), and 巻 (かん, 'volume'). The reading じょうげかん follows standard on'yomi readings for these kanji.