Quantum Mechanics: The branch of physics dealing with atomic and subatomic systems which describes nature at its smallest – scales of atoms and subatomic particles.
Quantization: The process where continuous quantities are broken down into discrete units. Like turning water flow (continuous) into ice cubes (discrete).
Energy Level: A quantized state that an atom's electron can occupy with specific energy values. Picture these like steps on a staircase, where each step represents a different energy level.