It's also perfectly acceptable (and preferred) if the code maps cleanly onto some existing mathematical terminology. 'v' is more readable than 'velocity' in the correct context.

Yes, single letter variables do have their place. But this place is very limited. Consider these lines in ruby

    data.reject{|e| e.value.nil?}

    data.reject{|element| element.value.nil?}

I would always prefer the first one. My general rule of thumb is: If a variable has the scope of exactly one line, or if it is an incremental counter, use one letter.

I’ll admit to a few larger funcs where I used one letter variables. It always starts with me thinking it will be a three-line routine, then It turns into a 30 line monstrosity that I don’t realize until I get a code review comment like “wtf is ‘zz = z’ about?”