Hi @shabbir5 ,

A semaphore is used on the platform to limit the number of transactions that can occur on a node at one time in order to protect resources on the node. When a user submits a request, it is routed through a semaphore pool where it basically joins a queue. If there is a free semaphore in that pool, then the request will grab it and process. When the transaction is complete, the semaphore is released and is free to process other requests that are in the queue.

Learn more from here : https://www.servicenow.com/community/now-platform-blog/troubleshooting-stuck-default-semaphores/ba-p...

https://www.servicenow.com/community/developer-forum/semaphore-what-is-it/m-p/1792091