one's own strength; one's own effort; by oneself
Emphasizes doing something using one's own ability or resources, without relying on others. Often used in contexts of self-reliance or personal achievement.
He solved the problem by himself.
Believe in your own strength and do your best.
A phrase composed of 自分 (self) + の (possessive particle) + 力 (power/strength). The meaning is transparent from its components.