There are many concurrent managers each monitoring the flow within each apps area.
but there are 3 MASTER CONCURRENT MANAGERS:
1. Internal Conccurent Manager (ICM): This is the one which monitors all other CMs
2. Standard Manager (SM) : This takes care of report running and batch jobs
3. Conflict Resolution Manager (CRM): checks concurrent program definitions for incompatability checks.
We cannot delete a concurrent manager... but we can disable it... but it's not recommended.