Dilution has two different meanings in trademark law.  One refers to illegally using someone else's famous mark, as described below under 'Dilution Statutes.'  The other use of 'dilution' is less common.  It refers to the degree to which a mark is, or has become, weakened.  This occurs from overuse of a mark.  Generally speaking, common words such as "tech" or "pro" are seriously diluted because they are used by multiple companies, even within the same industry.  When the first company used "tech" or "pro," the word most likely received very strong protection.  But, as more companies adopted these words for their marks, they lost a good share of their legal strength.

Finding out that a mark is diluted can be a mixed blessing for the trademark owner.   On the one hand, the owner will be able to join the multitude of others using similar marks.  However, when that owner wants to stop another from using a highly similar mark, doing so may be difficult or even impossible.

Even a mark that is highly distinctive, that would normally receive strong protection, may receive little or no protection because of dilution. Since a trademark owner generally wants to preserve the strength of their mark, and their ability to exclude others from using a similar mark, the owner must police and enforce encroaching uses of their mark, or else face that the mark may become diluted, possibly even abandoned.