is the time the system takes to deliver a shared resource from a releasing owner to an acquiring owner. Ideally, the Overhead time should be close to zero because it means the resource is not being wasted through idleness. However, not all CPU time in a parallel application may be spent on doing real payload work. In cases when a parallel runtime (for example, Intel® Threading Building Blocks, Intel® Cilk™, OpenMP*) is used inefficiently, a significant portion of time may be spent inside the parallel runtime wasting CPU time at high concurrency levels. For example, if you increase the number of threads performing some fixed load of work in parallel, each thread gets less work and the overhead, as a relative measure, will get larger. It is a basic application of Amdahl's Law.