what does Planck mean when he states that energy in quantized?
Ans: plank's theory proposes that the energies absorbed or emitted by atoms are quantized ,which means that their values are restricted to certain quantities.
is this O.K?
That looks ok to me but I might suggest a different word for quantized. My profs always told me that when defining a word or subject to avoid using that word in the definition. I would suggest "selective" but you may think of a better one.
Just as an after thought here, do you really understand how this thing works? You can't put this in the definition but let me explain how it works. Suppose we want to move an electron in shell #1 up to shell #2. It takes exactly x amount of energy to do that. Unless that packet of energy coming by the electron is just the right amount to move the electron to orbit 2 (or it might be enough to move it to orbit 3 or 4 or 5 etc) but the point is that it can't be some number in between. That is what is meant by quantized. That packet of energy must be the right amount or the electron pays no attention to it