_Function_: A _function_ is the smallest unit of a program in Fission.
It's a program with an function as an entry point -- it doesn't have
to be just one function.

_Trigger_: Triggers are what cause functions to be called.  For
example the HTTP trigger causes functions to be called on HTTP
requests.

_Instance_: Fission creates and runs servers containing these
functions.  The running server is called an _instance_.  You normally
don't need to worry about instances: their management is completely
automatic and transparent to you.  However, certain configuration
settings allow you to tweak the behaviour of instances -- for example,
you can configure the strategy for destroying unused instances.

_Generic Instance_: An instance with no user code in it.  The process
of including the user code to a Generic Instance is _Specialization_,
and the resulting instance is a _Specialized Instance_.

_Specialized Instance_: See _General Instance_.