The region of kernel code that must run atomically to prevent the data corruption which we calls it as "critical section's". When two or more threads try to execute that critical section's simultaneously, it is considered as a bug, that may lead to unexpected behavior, this situation we calls it as "race condition"
To prevent such race conditions on critical sections and preventing concurrency in kernel code is called "synchronization". Using these synchronization techniques guaranteeing that race conditions do not occur.