What is Priority Inversion in the Context of Real Time Scheduling?

When a lower priority task is already holding a resource, a higher priority task needing the same resource has to wait and cannot make progress with its computations.

The higher priority task remains blocked until the lower priority task releases the required non preemptable resource.

In this situation, the higher priority task is said to undergo simple priority inversion on account of the lower priority task for the duration it waits while the lower priority task keeps holding the resource.