A critical sections is a memory area to which only one task has exclusive access. To control access by tasks to critical regions, the database system uses special semaphores, which are called regions. When a task accesses a critical section, the associated region blocks this critical section for all other tasks.
Blocking critical sections has nothing to do with the SQL locks on database objects.
See also:
OLTP Console: Critical Sections
liveCache Console: Critical Sections