prescriptivists are people who are very set to the rules of grammar, and think that language is only proper when it has these rules. f.e. ending a sentence with a preposition or using the passive voice
descriptivists are people who think that that stuff isn't too important, and that they're very lenient about what is right and what is not. for example, a descriptivist would say that "a red big barn" is alright to say, and a prescriptivist would not, saying it should be "a big red barn."
it's important not to be either but find a good middle ground

what was the wikipedia article

Wow, you're good. I like this.