antaḥkaraṇam
The mind; the instrument inside.
In Vedanta
The inner instrument — the total mind with its four functions: manas (deliberation and doubt), buddhiḥ (determination and decision), ahaṅkāra (I-sense), and cittam (memory). The antaḥkaraṇam is inert (jaḍa) by nature but appears conscious due to the reflection of ātmā in it (cidābhāsa). It is the upādhi (limiting adjunct) that makes the limitless ātmā appear as a limited jīva.