It’s a custom “Kismet Node”: A new, community-hosted Unreal Engine Wiki - Announcements and Releases - Unreal Engine Forums
The turn-around thing about this node is that it can actually generate C++ classes and invoke functions from the generated classes by itself.
In general Kismet Nodes (or the UFUNCTION(…) ones) only know about C++ functions that already exist.
This node in particular creates an Unreal Object to store the code the user typed, then in runtime it already knows the pointer in memory to the compiled version of the function to call.
At runtime the node de-references the pointer and calls the “Execute” function of its object…
So you can have N^ custom Kismet Nodes packed into this only one node, instead of need to create one custom Kismet Node for each execution object you have.