Abstract: Quantum entanglement is a kind of nonlocal quantum correlations that has been widely used in quantum information processing. Recent studies have found that quantum (non-classical) correlations can exist even in separable states, and quantum entanglement is just one form of quantum correlation. Non-entangled quantum correlations play important roles in various quantum communications and quantum computing tasks. In this article, we briefly review the basic concepts of quantum correlation, introduce some commonly used measures of quantum correlation, and describe various applications and recent developments, together with several important references.