A more thorough explanation:

Dilution is a legal term that refers to the use of a trademark or trade name in a way that confuses or diminishes the public's perception of a famous mark. This can happen when a company uses a mark or trade name that is similar to a famous mark, causing consumers to be confused about the source of the product or service.

An example of dilution is when an appliance company puts white apple logos on their appliances, confusing consumers as to whether Apple began creating completely new items. This can harm the reputation of the Apple brand and diminish its distinctiveness.

Dilution can take two forms: blurring and tarnishment. Dilution by blurring occurs when the distinctiveness of a famous mark is impaired by association with another similar mark or trade name. Dilution by tarnishment occurs when the reputation of a famous mark is harmed through association with another similar mark or trade name.

Many countries around the world provide dilution protection in some form as a part of trademark law. In the United States, the Federal Trademark Dilution Act (FTDA) creates a federal cause of action to protect famous marks from unauthorized use. The owner of a famous mark is entitled to an injunction against another person who uses a mark or trade name in commerce that is likely to cause dilution of the famous mark regardless of the presence or absence of actual or likely confusion, of competition, or of actual economic injury.

To establish a claim of dilution, the mark must have become famous before use of the allegedly diluting mark or trade name began. Factors for determining whether a mark possesses the necessary degree of recognition include: the duration, extent, and geographic reach of advertising and publicity of the mark; the amount, volume, and geographic extent of sales of goods or services offered under the mark; and the extent of actual recognition of the mark.

Certain uses of famous marks, such as fair use, are not actionable as dilution. Fair use includes use of the mark other than as a designation of source for the goods or services in connection with: advertising or promotions that permit consumers to compare goods or services; and identifying and parodying, criticizing, or commenting on the owner of the mark or the goods or services connected with the mark. Also not actionable as dilution is use of a famous mark in any form of news commenting or news reporting, and any non-commercial use of the mark.