OpenStack what is the difference between driver and plugin

a)
Driver is a minimal implementation and Plugin is a complete specific implementation.

b)
Every driver will have a plugin, right ?

yeah, pretty much, although there are a couple of drivers / agents that use the ML2 plugin. So, it's not a 1-to-1 link

c)
Driver - Example ML2 Drivers . - ML2 is a plugin with the core implementation. All the Driver use a the results of core implementation.

Plugin - Example vmware, ml2, cisco, mlnx etc .. - Refer to individual specific implementation of a core abstract.