Difference between Element and Element Type

Hi, I am starting to learn Python in Dynamo with a toy example as shown below. I am wondering what is the difference between Element and Element Type. I noticed that the number of wall elements changed with the calling of WhereElementIsNotElementType(). Does anyone know the reason behind it? Thanks!

collector.dyn (3.1 KB)
The model used is the sample model provided in Revit (rac_basic_sample_project.rvt)

Element type is type of elements and Elements is every instance of the element type.

For more information

Thanks for the information @_Vijay . But I am still confused. More specifically, what does “WhereElementIsElementType” mean? The API doc says “Only elements that are ElementTypes will pass the collector”. What is “elements that are element types”…
In the script example if I don’t call this method it would be like this, including Autodesk.Revit.DB.WallType and Autodesk.Revit.DB.Wall.