The question should be: "what are arcs, chapters and episodes ?"
The order is: Arc>Chapter>Episode. The episodes are release in Young Animal and are usually made of approximatively 20 pages. The chapters are containing several episodes, and represent a continuity in the story (the Lost Children chapter for example). Finally, the arcs are made of several chapters (or just a lot of episodes if there's no chapter, like in the first 2 arcs), and define some era in Berserk (like the Golden Age, Guts and the Hawks, etc).
Here's a summary:
["BLACK SWORDSMAN ARC"]
Black Swordsman -> Revenge 08
["GOLDEN AGE ARC"]
Revenge 09 -> Episode 094
[RETRIBUTION ARC]
(Chapter of Lost Children)
Episode 095 -> Episode 117
(Chapter of the Binding Chain)
Episode 118 -> Episode 125
(Chapter of the Birth Festival)
Episode 126 -> Episode 176
[MILLENNIUM FALCON ARC]
(Chapter of the Record of the Holy Evil War)
Episode 179 -> Episode 235
#(Chapter of the Oblivion Herbs)#
DreamCast Game: between Volume 22 and Volume 23