PHP: What does a two dimensional and three dimensional array look and act like..?

I was looking online for the array tutorial but can't seem to get the concept!? Can someone explain two, three, dimensional arrays for me?

2D means you have an array of arrays, and 3D means you have an array of arrays of arrays.

2D:

PHP Code:

---

$foo = array(
  array(1,2,3),
  array(4,5,6)
); 


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3D:

PHP Code:

---

$bar = array(
  array(
    array(1,2),
    array(3,4),
  ),
  array(
    array(5,6),
    array(7,8)
  )
); 


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