来回通信延迟（Round-trip delay time），在通信（Communication）、电脑网络（Computer network）领域中，意指：在双方通信中，发讯方的信号（Signal）传播（Propagation）到收讯方的时间（意即：传播延迟（Propagation delay）），加上收讯方回传消息到发讯方的时间（如果没有造成双向传播速率差异的因素，此时间与发讯方将信号传播到收讯方的时间一样久）

In telecommunications, the round-trip delay time (RTD) or round-trip time (RTT) is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received. This time delay therefore consists of the propagation times between the two points of a signal.