Reformatting
Strictly speaking, reformatting is a process by which a Transformer's body is altered, almost instantaneously, from a mechanical to a technorganic form. In common, casual use among fans, the term is often applied more widely to any "instant" body change, including for example G1 Megatron's rebirth as Galvatron and the creation of the Cybertron Defense Team.
Fiction
Beast Machines
The term was introduced in the premiere of Beast Machines, titled "The Reformatting". The Oracle reformatted Optimus Primal and granted him the ability to reformat other Transformers merely by touching them and concentrating. Additionally, later in the series the Vehicon general Jetstorm was reformatted (restoring Silverbolt's conscious mind in the process) when Blackarachnia brought him into prolonged contact with organic goo from Cybertron's core.
When reformatted, each Maximal became technorganic, a tightly-woven amalgam of technological and organic components. This both bypassed Megatron's transformation lock virus, and gave them newfound weapons and abilities. It was also the penultimate step in an elaborate plan by the Oracle to reformat the entire planet of Cybertron.
At the end of the series, Primal and Megatron fell into Cybertron's organic core, which initiated the planet-wide reformat that left Cybertron a technorganic paradise.