Binary bonding

In the Generation 1 continuity family, binary bonding is a process in which a Transformer enters into a symbiotic relationship with a smaller, organic being (usually an Earth human or Nebulan) who has been augmented with the ability to transform into a component or weapon. It was by this process that the Headmasters, Targetmasters and Powermasters came into being.

From Teletraan I: The Transformers Wiki, a Wikia wiki.