Unconditionally or categorically; often used in the phrase '一概に〜ない' to mean 'you cannot say X in all cases' — i.e., not uniformly or without exception.
結果はケースバイケースで、一概に言えない。
The results vary case by case; you can't generalize.
高い給料が必ずしも幸せにつながるとは一概に言えない。
You can't say that a high salary always leads to happiness.
一概に賛成するわけではないが、提案には良い点もある。
I'm not unconditionally in favor, but the proposal has good points.