ATL::CStringT<wchar_t, StrTraitMFC_DLL<wchar_t, ATL::ChTraitsCRT<wchar_t>>>

This is a type definition in the Microsoft Foundation Class (MFC) library used for working with wide character strings (strings that use the wchar_t data type).

The ATL::CStringT class template is used to represent a string of characters. The first template parameter, wchar_t, specifies the character type (in this case, wide characters). The second template parameter, StrTraitMFC_DLL<wchar_t, ATL::ChTraitsCRT<wchar_t>>, specifies the string traits class that defines how the string is stored and manipulated.

The StrTraitMFC_DLL class is used to specify string traits for MFC dynamic-link library (DLL) projects. The second template parameter, ATL::ChTraitsCRT<wchar_t>, specifies that the string should use the C runtime library (CRT) functions for character manipulation.