What is a quadratic simultaneous equation?

Hello all!

I want to understand what a quadratic (or nth power) simultaneous equation (equation system) is...

It's clear that it's not only quadratic if the part equations are quadratic. I mean: {xy=3; x+y=4} is also called quadratic, despite the parts xy and x+y are not quadratic.

So how can you define a quadratic sim. eq.?

Is it quadratic if the biggest number of variables multiplied with each other is two? I mean xy=3 so x, y these are two and they are multiplied, so this is quadratic. But this also doesnt seem to be fine....

Help me out please!

Thanks and sorry for my English!