Hi there! I watched this movie several months ago and so my memory might be a little off but I did look at a Youtube video where one of the other people in the camp yells, 'We got a runner!' I think this scene is where our main hero first arrives and he takes off running as if to escape. So what that guy is referring to is that this new arrival is someone who tries to run and just escape when they first wake up. I would assume they have terms for different ways people react when they first arrive at the maze. In this case a 'Runner'. People who arrive and just start crying might be called a 'Weeper' or a 'Crier'. As for Slopper. This is a slang word for the movie universe I believe. Slang words aren't official words of languages and sometimes unique to a specific culture, region or group of people. For example I am from the Southern United States and we have all kinds of various forms of language and terms that mean something but aren't official words. The best known example of this is the word 'ain't' which isn't a word or contraction at all but is used to tell someone you are not going to do something. 'I ain't going to do it.' = 'I'm not going to do it'. So 'slopper' is some slang term or word used to define something in relation to that movie universe.

Runner - They run in the maze, looking for a way out. ( I think they are the smartest and fastest runner ) Sloppers : They do dirty tasks, houseworks, basically any job the Gladers do not want to do; treated as the lowest ranked job. This job is given to Gladers who are bad at every other job.