centre of power; power centre
Refers to the core group, institution, or location where political or organizational power is concentrated.
That politician is a person close to the centre of power.
A fierce struggle broke out within the party's power centre.
中枢 alone means 'centre' or 'hub' in a broader sense (e.g., 交通の中枢 'transportation hub'), while 権力中枢 specifically refers to a political or organizational power centre.
Compound of 権力 (けんりょく, 'power') and 中枢 (ちゅうすう, 'centre, hub').