What does it mean to say “linux kernel is preemptive”?

Question

I read that Linux kernel is preemptive, which is different from most Unix kernels. So, what does it really mean for a kernal to be preemptive?

Some analogies or exam

Answer 1

I think it became preemptive from 2.6. preemptive means when a new process is ready to run, the cpu will be allocated to the new process, it doesn't need the running process be co-operative and give up the cpu.