A continuous-time Markov chain (CTMC) is a stochastic process that models systems undergoing transitions between states at continuous time intervals, where the future state depends only on the current state and not on the sequence of events that preceded it. This memoryless property is known as the Markov property, and CTMCs are widely used in fields such as queueing theory, population dynamics, and reliability engineering to model random processes that evolve over time.