Aphorism:
A terse statement of known authorship which expresses a general truth or a moral principle. (if the authorship is unknown, the statement is generally considered to be a folk proverb.) An aphorism can be a memorable summation of an author's point, or it can be a focusing device at the beginning of the essay.

Example: 
"Be kind, for everyone you meet is fighting a hard battle."
-Plato

Explanation:
 This quote, said by Plato is a prime example of a Aphorism. He states a moral principle, of being nice, but in his own way. The purpose of this is to go right to the point, and tells you the general truth plain and simple. It shows Plato's views, and doesn't beat around the bush in order to do so.