Sparks

A Spark (スパーク, Supāku) is the lifeforce, or soul, of a Transformer. Each spark is part of the essence of both Primus and the AllSpark themselves.

The spark is a physical entity which is safeguarded inside a Transformer body. If something harms the spark beyond repair, it is "extinguished" and returns to the Well of the Great Sparks. The Transformer is then considered dead. A Transformer is able to survive an enormous amount of physical damage. As long as the spark is intact, it is possible to repair or rebuild the body and restore the spark to it.

Aberrant sparks
Some sparks have exhibited properties or behaviors that do not seem to be generalizable to other sparks.