Trope

A Trope is a device used in storytelling to quickly get an idea across to the audience.

A very comprehensive guide to various tropes used is the TV Tropes wiki.

Be forewarned, though; that site is extremely addictive due to the fact that it has hundreds of pages, all with examples using various continua. It should be noted that tropes are not the same things as clichés. In other word, Tropes Are Not Bad.