Sooner or later; eventually — an adverb expressing that something will happen in due course (more emphatic than いつか/何時か).
いつかは自分の店を持ちたいと考えている。
I hope someday I will have my own shop.
この問題もいつかは解決するだろう。
This problem will probably be solved eventually.
いつかは故郷に帰るつもりだ。
Someday I intend to return to my hometown.