I think you meant to say "single pilot passenger jet" that is fully certified, and if so, that statement is not correct. The Phenom, Citation, and several others are.

For a layman, what does certification mean? Certified for what?

I suppose GP meant to say “single engine non-turboprop turbofan/turbojet private jet that are FAA certified to operate in the US with appropriate civilian licenses”.

And while there are countless single engine jet planes and many small business jets without lavatory, there indeed aren’t many (“jet” engine && single engine && business jet) designs, let alone civilian type certified models.

Certification is the process of getting an aircraft design/model approved by the FAA for sale/use. There are 3 phases for GA commercially available aircraft, type certification (design approved), production certification (manufacturing approved), and airworthiness certification (plane tested, and ready for sale to the public)

Usually when someone says a plane has received its certification they mean it’s ‘airworthiness certification’, so the final approval by the FAA.

Each commercially ised or sold aircraft has to come from a certified Desogn Organisation, has to be built by a certified Production Organisation (in most cases the same company, aerospace legallish Airbus and Boeing have a DO and a PO which arw separate entities as far as authorities are converned), needs an Type Certificate (achieved after successful flight testing and to be redone if there are configuration and design changes) and has to be maintained by a certified maintenance organisation and operated by a certified operator (continued airworthymess is a operator thing, just don't ask me any details on that, I work on the PO and touched some maintenance stuff in my life so far).

Usually, EASA and FAA cross certify, making it easier to get one if you have the other already. Fascinating stuff, aerospace certification.

Boeing skipped the step "to be redone if there are configuration and design changes" for the 737MAX, and smoothed over the differences with software. FAA was supportive of that rule-bending, and other countries followed along.

Yes and no. They din't skip it, the FAA acceptrd and certified the new design based data Boeing provided. Boeing should have, in my opinion, completely recertified the MAX instead of treating it as just a new 737 variant.

Single engine is more likely what the poster meant than single pilot, no?

that’s what i meant.

what makes this plane unique is its single jet engine. this also makes running costs lower.

Ah, ok. There is another one coming, which will be neat. Right now it's an EAB but they're working towards type certification. https://www.stratosaircraft.com/716-aircraft