User blog comment:QuasarBooster/Extra-Growth Hierarchy, extension of FGH/@comment-25601061-20150711171756/@comment-24923514-20150711204740

It indicates a possible remainder of a list. For example, the expression $$\text{Ex}_{0,1,0,2}(1)$$ has a list of subscripts (0,1,0,2). The two rightmost entries are to be evaluated first when expanding this expression, while the (0,1) part would be the rest of the list, or •