why last?

Most programmers tend to name their functions and variables something descriptive. A name that will give a hint to its purpose, or maybe how its used.

Looking at this function, the name tells me that its a function to check whether or not the node was rendered in the previous(last) frame.

I don't know why they care. Why don't you see where that value is actually used? Chances are that that function simply sets a boolean variable in the class... search through the source code for where that variable is used.

Offtopic: do you realize that you've posted EIGHT topics today? Just out of curiosity, what do you do to try to answer your own questions before posting them here?

Absolutely, we should all solve our own problems and not post anything here. ;)

It's for optimization. You would use it something like this:

    // If the object was rendered last frame, then it will probably be visible    // this frame too, so just draw it. Otherwise, test if it is visible before drawing.        if ( getRenderedInLastFrame()    {        Draw();    }    else    {        // Test if the object is visible. If it is, then draw it.                bool visible;        visible = ExpensiveTestToDetermineVisibility();        if ( visible )        {            Draw();        }    }