:I apologize for not giving a better explanation. I should add that some older definitions will list lymphocytes as nongranular or agranular because they are not including natural killer cells. I was taught (and have read) that this was simply because for a time after their discovery they were deemed to be just artifacts, then realized to be actual components of the immune system once again. Therefore, it's completely understandable why anyone would be unsure. To be exact, there are three groupings of lymphocytes: T-cells, B-cells, and null, the latter including natural killer cells. 
 However, it should be noted that a Wikipedia article should not state that lymphocytes are agranular and then only a part of the way down speak of "granular lymphocytes."