Quantum discord is a measure of the quantumness of correlations between two systems. It arises from the difference between two classically identical expressions for mutual information, which differ when the systems are quantum. This difference quantifies the quantum excess of correlations, known as quantum discord. The concept is related to the quantum superposition principle and the idea of pointer states, which are stable states of a system that do not entangle with the environment. Decoherence leads to environment-induced superselection (einselection), which singles out pointer states and reduces quantum correlations. The quantum discord can be used to determine the preferred classical states of a system. The paper discusses the classical and quantum aspects of correlations, showing that separability does not guarantee classicality. A separable density matrix can still have non-zero quantum discord, indicating quantum correlations. The quantum discord is asymmetric and depends on the measurement basis. When discord vanishes, it indicates that the system has classical-like properties, allowing information to be extracted without disturbing the state. The paper also presents a simple model of measurement to illustrate quantum discord. It shows that when the measurement basis corresponds to pointer states, the discord vanishes. The quantum discord is a measure of the information that cannot be extracted without joint measurements. It is a good indicator of the quantum nature of correlations. The paper concludes that minimizing quantum discord over possible measurements yields pointer states, which are stable and classical-like. The results are supported by mathematical proofs and examples, showing that quantum discord is a useful tool for understanding quantum correlations.Quantum discord is a measure of the quantumness of correlations between two systems. It arises from the difference between two classically identical expressions for mutual information, which differ when the systems are quantum. This difference quantifies the quantum excess of correlations, known as quantum discord. The concept is related to the quantum superposition principle and the idea of pointer states, which are stable states of a system that do not entangle with the environment. Decoherence leads to environment-induced superselection (einselection), which singles out pointer states and reduces quantum correlations. The quantum discord can be used to determine the preferred classical states of a system. The paper discusses the classical and quantum aspects of correlations, showing that separability does not guarantee classicality. A separable density matrix can still have non-zero quantum discord, indicating quantum correlations. The quantum discord is asymmetric and depends on the measurement basis. When discord vanishes, it indicates that the system has classical-like properties, allowing information to be extracted without disturbing the state. The paper also presents a simple model of measurement to illustrate quantum discord. It shows that when the measurement basis corresponds to pointer states, the discord vanishes. The quantum discord is a measure of the information that cannot be extracted without joint measurements. It is a good indicator of the quantum nature of correlations. The paper concludes that minimizing quantum discord over possible measurements yields pointer states, which are stable and classical-like. The results are supported by mathematical proofs and examples, showing that quantum discord is a useful tool for understanding quantum correlations.