Share what you've learned about C++.
From the announcement:
Have you learned something interesting about C++, maybe a new technique possible in C++14/17? Or perhaps you have implemented something cool related to C++, maybe a new C++ library? If so, consider sharing it with other C++ enthusiasts by giving a regular program talk at CppCon 2018.
The submissions deadline is May 11 with decisions sent by July 1.