Prose refers to comedies written like a novel, for example
Tahu walked into the house. He saw Kopaka sitting on a couch reading a magazine.
"Hey Kopaka," Tahu asked, "How you doin'?"
Kopaka looked up from his magazine, his face emotionless. "I'm a bit... chilly." he said.
Tahu stared at him blankly. "I don't get it." Tahu replied.
Kopaka sighed and looked back into his magazine. "I didn't think you would." he said.
Prose comedies are basically written he said/she said. Characters speak in between " and " (66's and 99's). Sometimes they are considered more serious (and are often the choice for writers of the Epicomedy(although many epicomedies are written in Script), although it's always easy to find a prose comedy that's as silly as they get.
Prose comedies usually have large sections where no one speaks, and the author goes on, describing what the characters are doing, what the scene looks like, etc.
It is usually easier to reach the 300 word limit using prose, although that is often overlooked by new writers, as script appears easier. With prose, it's quite easy to reach 3000-5000 words in a chapter (such as the first few chapters of Transonicle 3). Prose however, does relie on a certain mastery of the English language, considering you need to be able to write fairly coherently in order for what you wrote to be read. Microsoft word is recamended for prose, otherwise your writing can easily become incoherent blobs.