SDET stands for Software Development Engineer in Test or Software Design Engineer in Test, this kind of role is originated from Microsoft and currently many organizations are demanding such SDET professionals who can participate in development of the application and also in testing of the software developed.
SDET is a benchmark used in the systems software research community for measuring the throughput of a multi-user computer operating system.
Its name stands for SPEC Software Development Environment Throughput (SDET), and is packaged along with Kenbus in the SPEC SDM91 benchmark.
A more modern benchmark that is related to SDET is the reaim package, which is itself an up-to-date implementation of the venerable AIM Multiuser Benchmark.