How to find out if planes are perpendicular

Determine if planes in each pair are parallel, perpendicular, or neither.

$\displaystyle \pi_{1}: 4x-5y+z-9=0$

$\displaystyle \pi_{2}: 2x-9y+z-2=0$

This is what I did

n1 :[4, -5, 1]

n2:[2, -9, 1]

Dot product of n1 and n2 is not zero, so it's neither?

$\displaystyle \pi_{1}: 5x-6y+2z-2=0$

$\displaystyle \pi_{2}: 2x-5y+-20z-2=0$

This is what I did

n1 :[5, -6, 2]

n2:[2, -5, -20]

Dot product of n1 and n2 is zero

What does that mean, is it parallel or perpendicular?

and how do you find out if it's parallel or perpendicular

Thanks