I think on this one many people are going to pick games like Lazers with Feelings or Fate Accelerated because they are going to reply in the most literal sense. While both Lazers and Fate are both indeed some of the shortest worded RPG games you will ever have the pleasure to come across. I do not think that we are talking about what they do in their word count here.

Monte Cook Games Cypher System with its.

I am (adjective)Descriptor  (noun)Type  who (Verbs)Focus’s 

The power of this single sentence might do the most with the least amount of words in the history of any RPG. With developing everything they way they did around Type Descriptor and Focus you not only have a natural way to convey to everyone at the table who you are and what you are known for. But you also in a just once sentence have simultaneously given the players a Roleplaying description of your character as well as told them what your character is capable of stat and power wise.

Now to be fair and in the interest of wanting a slightly longer blog post, I also mentioned Lazers and Feelings as it literally created the genre of single page RPGs.