Wave-particle duality: Particles such as electrons and photons exhibit both wave-like and particle-like properties. This means they can behave as waves, with characteristics such as interference and diffraction, and as particles, with localized positions and momenta.

Uncertainty principle: Formulated by Werner Heisenberg, this principle states that certain pairs of physical properties, such as position and momentum, cannot be precisely determined simultaneously. The more accurately one property is known, the less accurately the other can be known, introducing inherent uncertainty into the description of quantum systems.

Quantization: Certain physical quantities, such as energy, angular momentum, and electric charge, are quantized, meaning they can only take on discrete, specific values rather than continuous ones. This leads to phenomena like discrete energy levels in atoms and the quantized behavior of electromagnetic radiation.

Superposition: According to quantum mechanics, particles can exist in multiple states simultaneously, a phenomenon known as superposition. For example, an electron can be in a superposition of multiple positions or energy states until it is measured and its wave function collapses to a single state.

Entanglement: When two or more particles become correlated in such a way that the state of one particle cannot be described independently of the others, they are said to be entangled. Changes to the state of one particle instantaneously affect the state of the others, regardless of the distance between them, a phenomenon famously described as "spooky action at a distance" by Einstein.