TITLE: Summation symbol with just one letter below it? How to verbally state.
QUESTION [5 upvotes]: I'm used to seeing summation capital sigmas with a "start" at bottom and a "stop" at top and would say the sum from i to 100 or whatever. But in this case, there is just a y at bottom. 
How would I write this out so a screen reader would be able to read it aloud and get the correct idea across to the listener?

REPLY [3 votes]: It depends on context.  Sometimes it means "sum over all possible values of $y$" (where which values of $y$ are allowed should be clear from the context), but sometimes it means an indefinite sum or "anti-difference", analogous to an indefinite integral or antiderivative:
$$ \sum_y f(x,y) = g(x,y)\ \text{where}\ g(x,y+1) - g(x,y) = f(x,y) $$