Improper use of keywords is the fourth most common reason for App Store rejections. When you spend the time to come up with well thought out keywords for the audience you’re trying to reach, it increases the likelihood they will find your app on the App Store.

The most common rejections are for keywords which are offensive, objectionable words or phrases; using trademarks, company or product names, unauthorized use of celebrity names and/or likenesses; and irrelevant keywords (i.e., keywords not pertaining to the submitted application). Some examples:

• Suitable keywords: Puzzle, solving, game
  These keywords are directly applicable to the description of your application and its functionality.
• Unsuitable keywords: Racing, Fart, Bejeweled, EA
  These are all grounds for rejection as Racing and Fart are irrelevant and Bejeweled and EA are registered trademarks.

• Suitable keywords: Racing, drive fast, speed, NOS
  These keywords provide a description of the user experience and are related to your application’s features.
• Unsuitable keywords: Free, Nascar, Dale Earnhardt Jr.
  Using these keywords will cause your app to be rejected. The application is not free, Nascar is a registered trademark, and Dale Earnhardt Jr. is a well-known public figure. Without explicit rights from public figures you cannot use their names or likenesses.

• Suitable keywords: Learn, master, study, lessons, Spanish, quick reference, Spain, español, travel, 3.1
  These keywords connect with interested searchers’ likely frame of mind, 3.1 is appropriate since it’s the minimum iPhone OS version.
• Unsuitable keywords: Date, Rosetta Stone, Dutch, French, 3.0, 2.2
  Rosetta Stone is a registered trademark, dating has nothing to do with the application, and it does not teach Dutch or French. Since the minimum OS version of this apps is 3.1, users would not be able to install it if they are running iPhone OS 3.0 or earlier.
  

You can learn more by reading the App Store Quick Reference: Assigning Keywords For Your App

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