Now that Blade Runner 2049 came out, my perception of what a replicant is has been completely blurred.
To start off, the first Blade Runner established that Replicants are bio-engineered robots. So I assumed they're like terminators - human flesh on the outside with metal and circuitry on the inside. There is even a scene where Roy Batty drives a nail through his hand, when it stopped working, presumably to fix circuitry issues.
But with the new Blade Runner 2049, we learn that Replicants have human bones, human flesh that can decompose, and human traits of reproduction. Not only that, they can have children with humans (we don't really know whether Deckard is replicant or not, so I can make that argument).
So are replicants just humans with shorter (or longer) life expectancy? Or are they "robots", and how?