So many names to that block. Some call it Split QST.

I call it a "y" block because the seams form the letter "y" or the mirror of it.

I've always known it as a Boston Block or a Quarter Square Triangle Block. You can do lots of things with that block. Put them together one way to make twisted ribbons or another way to make pyramids.

I have learned to call it a Boston Block, probably from this board. lol