By definition, a cliché is a phrase or a sentence which has been overused to the point that the phrase or sentence holds no true meaning. Essentially, clichés, prior to their overuse, had true meaning. After years, or decades, of repetition, the phrase or sentence came to meaning nothing at all (in regards to the original meaning or emotion which the phrase was meant to elicit).
Clichés can be the tell-tale sign of a novel writer (given prolific writers stay away from clichés--unless used to elicit a specific effect or in dialogue). Many times, clichés are created to bring about a certain effect. That said, once the phrase or sentence is successful, the phrase or sentence begins to be overused and the phrase/sentence becomes a cliché.
The word cliché is of French origin. Cliché, in French, refers to a block or plate used for printing. Printing plates are reused in order to recreate the same thing time and time again. Over time, the plate (due to use) becomes worn and no longer usable. Like the English use of cliché, the phrase/sentence has become overused and no longer "works" as it was originally intended.
The second link below offers examples.
an expression or element of an artistic work
A trite expression, often a figure of speech whose effectiveness has been worn out through overuse and excessive familiarity.
Stay the course.
A cliche is overused phrase, expression, idea, or storyline. The word also usually means an idea which used to be unique or brilliant, but due to everyday use and misuse of people, have become something predictable and unoriginal.