Moving from one process state(like Ready state, running state, termination state) to another process state. Process transition may occur due to different purposes like if a process: waiting for I/o operations, waiting for data from disk(moved to blocked state from running state and stays there until data extraction process in not over), or if there left no instruction in the process to be executed....then it moved to termination state from running state, If a process is in running state and at that time it is interrupted by another process, then process move from running state to ready state(join queue again and waiting for its turn again).

explain process, pcb and process state diagram.

what is steady state flow process in fluid dynamics

There is no such process.

In computing, if a processor is running and doing a number of activities, those activities are known as its states. As a processor executes, its state changes. There are number of states like New state i.e. creation of new process, Running state i.e. execution of instructions, Waiting state i.e. its a state where processor is waiting for some activity to occur, Ready state i.e. in this a particular process has acquired the resources and is waiting to be assigned to a processor, Terminated state i.e. the execution of a process has completed.