OK! First of all, a "zero" is where a graph crosses or touches the x-axis.
They're called "zeros" because that's where y = 0 !
*Officially, these are called "real zeros".
Here are some questions for you:
Can we draw a parabola (a 2nd degree polynomial) that
|touches the x-axis twice?|
|touches the x-axis once?|
|never touches the x-axis?|