Polygenic is exactly what the word indicates. It means many genes. A polygenic trait needs numerous genes to align in order to be displayed. They are not as simple as a simple recessive or co-dom.
Some polygenic traits are strong or more simplistic and easy to replicate while others are much more involved and not easily reproduced. In other words, some are more reliably reproduced than others and do not need copies of the genes from both parents. One parent can pass the genetics down to its offspring.

A polygenic trait can act almost like a recessive or co-dominant but the mode of inheritance is way different.