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.
独力 also means 'one's own effort', but is less common and slightly more literary than 自分の力.
A phrase composed of 自分 (self) + の (possessive particle) + 力 (power/strength). The meaning is transparent from its components.