Stratum 3 is a layer in the Internet hierarchy of timekeeping systems, primarily used for synchronizing clocks. It receives time signals from Stratum 2 servers and distributes them to Stratum 4 devices. This layer is crucial for maintaining accurate time across various networks and applications. Typically, Stratum 3 servers are connected to reliable time sources, such as atomic clocks or GPS systems. They ensure that the time provided to lower strata is precise, helping to coordinate activities in fields like telecommunications, finance, and computing, where accurate timing is essential.