There are few System Cache Tables gets created when you bring up the Pega application. Those Tables store the Application, Administartion and Node status related information like temporary cache to drive the components what is necessary. Most frequenctly used such Tables listed below and Pr_sys_delayed_queue is one of them.
Those DB Tables use to be truncated when the Pega Application is kept under maintaineance in-order to let the application start smoothly. All the above information are useful in the Pega Administration perspective. Let me know if you need more help.
It's not derived from pr_sys_delayed_queue or from any other table. It's a general purpose of the few sys tables which stores the cache information and we, administrators use to clear / truncate them during the maintenance. But, looks to me that, PR_SYS_DELA_temp is a DB Table created manually and i do not see the DB Table in our system.
If, you had to truncate the DB Table: PR_SYS_DELA_temp, Better create a backup of the same DB Table and proceed for truncation.