The position of the rigidbody.
Rigidbody.position allows you to get and set the position of a Rigidbody using the physics engine. If you change the position of a Rigibody using Rigidbody.position, the transform will be updated after the next physics simulation step. This is faster than updating the position using Transform.position, as the latter will cause all attached Colliders to recalculate their positions relative to the Rigidbody.
If you want to continuously move a rigidbody use MovePosition instead, which takes interpolation into account.