Some people get their super-powers from an origin. That is, it's an essentially random and apparently unrelated event, such as being bit by a radioactive gerbil, sleeping in a toxic waste dump, being struck by lightning or similar. Origin heroes can have just about any powers, although there is a tendency for them to be Bricks.
They are the people that exist who have some of the genetic encoding to be a mutant but not a complete 'set' such that the puberty process is sufficient to manifest powers. In rare instances, some outside event (getting hit by lightning, being exposed to a vacuum, chemical or radiation) can result in a manifestation as if that person were a mutant - the event generating the switches that didn't exist completely in the genetics and the shock stress of the trauma substituting for the chemical influences of puberty.
- That is why Origins are more unstable, power wise (especially at first). Their bodies don't benefit from the whole package implied in the genetics as a survival set... For instance, an Energizer is likely to manifest in a way that they can throw lightning and will probably be empowered by electricity in general... or at least immune/resistant to damage from an errant electrical charge. An Origin who can throw lightning may not be protected in any way from an ability gained as the result of a lightning strike. The event toggled the genetics for the ability to channel and direct the bolts, but there's no guarantee they can also hold a multi-bolt level of charge.