Usually this means that it is a street legal car that is/was sold to the public.
In modern times this also means that it went through crash testing so modern production cars have much larger production runs to offset the costs of that or are very very expensive (millions). For example Rimac said they are planning to make 150 Neveras but they also had to make multiple rolling bodies and a couple fully built cars (at minimum one for EU and one for US if you want to enter both markets) for crash testing on top of any development cars.
But strictly speaking there is no one definition but instead each field/industry defines it in its own way. Motorsports has its own (multiple actually depending on the series/governing body), car manufacturers have their own, record keeping organisations have their own (guinness book of records), etc
In the sense that it is "homologated" and has had to pass all of the same tests as a car that will sell in the hundreds of thousands, or even millions of units.
I feel like the minimum standard is too low, tbh. Building dozens of them and selling them seems like enough.
There needs to be another standard that is something like... built at least 10k of them. Because less than that is still likely hand-built and it doesn't really mean much that it was "production".
It's hand built. And it would not surprise me if every one of them is different.
I can buy a Caterham-7 and drive it on public roads too. That doesn't make it a production car even though it is probably much more standardised than the Koenigsegg.
In modern times this also means that it went through crash testing so modern production cars have much larger production runs to offset the costs of that or are very very expensive (millions). For example Rimac said they are planning to make 150 Neveras but they also had to make multiple rolling bodies and a couple fully built cars (at minimum one for EU and one for US if you want to enter both markets) for crash testing on top of any development cars.
But strictly speaking there is no one definition but instead each field/industry defines it in its own way. Motorsports has its own (multiple actually depending on the series/governing body), car manufacturers have their own, record keeping organisations have their own (guinness book of records), etc