Update: See how Google Play Short Description best practices have changed since this article was written. Using the pyramid analogy from our post on naming an app, the short description has limited space and as such, carries more weight in the indexing of an app on Google Play when compared to the bigger "full description" field. Those familiar with SEO might equate the short description to a combination of the indexation benefits of using headers (H1, H2 etc..) and the conversion benefits of the meta-description field. Number 2 below shows where the short description is displayed in the Google Play app listing from a mobile device.
Google Play Guidelines
Not to be confused with the full description - which allows 4,000 characters, the Google Play short description is limited to 80 characters. This field was previously named "Promo text" and serves much of the same purpose today. The short description is the first bit of text potential users see in an app listing when in the Google Play app. Once a user has installed the app, the short description is replaced by "what's new" text. More information on restrictions and guidelines can be found here.
Feature-based Marketing Copy
The short description is a unique field to Google Play (Apple does not have promo text or short description). Like most of the elements of an app listing, the short description impacts how an app is indexed and how well it converts viewers into users. Assuming the most important feature or target phrases are in the app's title, the short description provides space for introducing additional features using targeted keywords and phrases. For elements in an app store listing that affect conversion, we recommend working with focus groups to determine which versions of these elements convert your target audience best.
Learn more about Short Descriptions and how to utilize them for App Store Optimization.