PROSE

Prose is one of kind of literature. The term “prose” originates from the Latin prosa, meaning "in phrase" which was derived from prosa oratio, meaning "straight, direct, unadorned speech." This phrase was derived from prorsus, meaning "straightforward or direct" and can be further traced to pro versusm, meaning "turned forward."

 According to Wikipedia, Prose is a form of language that possesses ordinary syntax and natural speech rather than rhythmic structure; in which regard, along with its measurement in sentences rather than lines, it differs from poetry. (https://en.wikipedia.org/wiki/Literature )

Another definition, It is also defined to be as the epic literature that is written in lines. It is basic literature that is seen and used daily. Prose includes books, such as novels, tales, and short stories. Like any other literary work, it has different characteristics, and rules and regulations that make up the prose.
About characteristics, there are characteristics of prose which divided by purpose :
1.     Narrative: writing which tells a story (can be fiction or non-fiction); usually told in chronological order; has characters; follows the basic plot-line - exposition, rising action, climax, falling action.
2.     Expository: gives basic information; used often in speeches and essays; does not tell a story or argue.
3.     Descriptive: describes something in detail, again without telling a story or arguing a point; used most often in combination with another mode of writing, but alone is often found in scientific or medical reports.
4.     Persuasive: argues a point (or two sides of a question); gives evidence in favor or against.

Actually there are many types of prose, it even include essays, letters, editorials, articles, and journals.

Some Common Types of Prose

1. Nonfictional Prose: A literary work that is mainly based on fact although it may contain fictional elements in certain cases. Examples are biographies and essays.
2. Fictional Prose: A literary work that is wholly or partly imagined or theoretical. Examples are novels.
3. Heroic Prose: A literary work that may be written down or recited and employs many of the formulaic expressions found in oral tradition. Examples are legends and tales.
4. Prose Poetry: A literary work which exhibits poetic quality using emotional effects and heightenedimagery but are written in prose instead of verse.

So I can conclude that Prosa is a writing which is written just with ordinary grammatical and natural speech. Although like that, it does not lose the literature values and still nice to read.

References :
https://en.wikipedia.org/wiki/Literature
http://literarydevices.net/prose/
http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Prose.html