man page for sem_overview tells (with description how to do it) :

POSIX semaphores allow processes and threads to synchronize their actions.

therefore semaphores can be used for interprocess communication.

well in linux there are basically two types of semaphores

named semaphores
unnamed semaphores

and I think here unnamed semaphores is basically known for IPC mechanism plus locking mechanism both.and named one are only used for locking mechanism

this link can be useful

I think the reason is because of named semaphores.
There are two types of semaphores, named and unnamed.

Usually named semaphores are used for processes synchronization, whereas unnamed semaphores are used for threads synchronization.

This Multithreaded Programming Guide says

Named semaphores are like process-shared semaphores, except that named semaphores are referenced with a pathname rather than a pshared value. Named semaphores are sharable by several processes.

*It is possible to share unnamed semaphores (with child processes for example) among process but it is not common.