Dictionary meaning of concurrency: the fact of two or more events or circumstances happening or existing at the same time.
What is concurrency?
Concurrency refers to the parallel processing. It is the ability to execute more than one programs or more than one parts of the program in parallel without affecting the final outcome.
Note: Threads are the backbone of java concurrency.
A process has a self-contained execution environment i.e. allocates separate memory area. Context switch time is more in case of processes because switch is done between different memory areas.
A thread is a lightweight process. Thread uses process’s execution environment i.e. memory area. Context switch time is less in case of threads because switch is done within the same process’s memory area.
Process vs Thread
Note: By default, a java application runs independently in one process. We need to use several threads to achieve parallel processing in java application.