You can find more information about each of the items in the profiler hierachy by searching the engine source code for the corresponding occurrences of the SCOPED_DRAW_EVENT macro, which occurs within the block scope that the profiler time is attributed to.
So it looks like it refers to the time taken to render all of the DynamicMeshElements batches in the base pass of a given view - and DynamicMeshElements, in turn, appears to be a catch-all for any renderable geometry that isn’t a static mesh.
I just finished a video in which I explain majority of the categories in GPU Visualizer / ProfileGPU.
What I was curious about is what precisely affects their costs. For example what makes the Base Pass or ReflectionEnvironment longer in the first place and what is secondary. I made my best to ensure this info is correct, i.e. read engine code, did tests.
The link from @Neverender was also helpful as a starting point for Base Pass - thanks.