Question

What does it mean to say that something is quantized?

Answer 1

Electrons are quantized in their orbits. This means that they can change energy levels but only if the right quantum of energy comes along. They will accept the quantum of energy if it is the right amount to allow them to make the jump to the next energy level. They will ignore the quantum of energy if it is too much or too little.
http://hyperphysics.phy-astr.gsu.edu/Hbase/bohr.html