I always see that different stories in the same anime series are usually called with either "hen", "arc" or "season" as seen in the examples below.
- Hen (編)
JoJo no Kimyou na Bouken - Stardust Crusaders - Egypt Hen
Alps no Shoujo Heidi: Alm no Yama Hen
Hokuto no Ken: Raoh Gaiden Gekitou-hen / Hokuto no Ken: Raoh Gaiden Junai-hen
Arata naru Sekai: Kako-hen / Arata naru Sekai: Gendai-hen / Arata naru Sekai: Mirai-hen
One Piece: Arlong Park Arc / One Piece: Sabaody Island Arc
Bleach: Arrancar, The Arrival Arc / Bleach: Arrancar, The Hueco Mundo Sneak Entry Arc
Naruto: Chuunin Exam Arc / Naruto: Pain's Assault Arc
Aldnoah.Zero 2nd Season
Girls Bravo: First Season
Moonlight Mile 1st Season: Lift Off
I observed these differences:
Hen: Always added at the end of the title. Sometimes it is made suffix with a hyphen.
Arc: Used to logically divide long running series.
Season: Always used with a number starting from 1.
Why do they choose one over another? For example, why don't we say "Moonlight Mile: Lift Off Hen" or "Naruto: Chuunin Exam Season"? Is this only a matter of choice or do they differ in meaning?