Sparks

A spark is usually the "soul" of a Transformer in the fictional Transformers universe.

the fragments of the Matrix itself" the "well of all sparks" that currently exist, have existed, or ever will exist. Sparks leave the Matrix upon the birth of new Transformer life so that they may learn, grow, love and truly experience life, and then, with the passing of the Transformer, the Spark returns to the Matrix, assimilated back into it to share all the knowledge it has gained with the whole but their individuality is not extinguished.

In knowing this, it can be taken that the object known as the Autobot Matrix of Leadership, long stated to hold the wisdom of the ages, is a gateway to this realm, where the amassed knowledge it contains can be consulted (where the sparks of those who have formerly held the Matrix retain their individuality and can be communed with).