With VMware, hot add, hot plug and hot extend all describe the act of adding resources to a powered-on VM. What kind of "hot," however, depends on what type of resource you're adding to the VM.
In VMware parlance, you hot-add virtual memory (RAM) and network interface cards, hot-plug virtual CPUs and hot-extend the virtual disk. To avoid sounding like a beginner, admins should know which term to use with each kind of resource -- memory, processors, networking and disk -- although frequently you will hear "hot add" used to describe boosting any of these resources.
But be aware: Not every VM operating system supports hot-adding or hot-plugging.
Read more about adding hot resources
What you can do with hot add and hot plug
When to enable hot add