Please note that this is for Linux. Window has always had its own RAM management (non burstable).
Burstable RAM: If your VPS has bursting and requires additional resources, it will pull them from the available resource pool (this is a burst) and return them when they are no longer needed. So if you have a temporary spike, the resource pool will normally cover you.
SLM based RAM: If your VPS has SLM Management, in the event your VPS uses all of its physical RAM SLM will automatically delay the execution of processes to wait for more RAM to become available. After this it intelligently decides which processes to kill to maintain a running system. Kind of like having a manager watching your processes 24 hours a day.
On the kernel level it also decides what should be preempted to swap in the system and which data is most rarely used. This is more efficient from overall performance point of view.