These are related to services. We all know that services keeps on running in the background and they also consume some memory to execute.
So, as more of the application runs on android device, the device memory keeps on getting low and when the time arises, when the device memory gets critically low, the android system starts terminating processes, so as to release the memory occupied by the processes.
But you might be doing some important task with the services, that could also get terminated as the service stops. so these concepts are to tell the android system what action you want to perform when the device memory gets stable and when it is ready to relaunch the services.
The simplest explanation of these could be,
START_STICKY- tells the system to create a fresh copy of the service, when sufficient memory is available, after it recovers from low memory. Here you will lose the results that might have computed before.
START_NOT_STICKY- tells the system not to bother to restart the service, even when it has sufficient memory.
START_REDELIVER_INTENT- tells the system to restart the service after the crash and also redeliver the intents that were present at the time of crash.