Folks say that you should compare Apples with Apples and compare Oranges with Oranges. As it relates to Trademark Law, these comparisons can determine the relative strength or weakness of a Trademark.
One example of a weak Trademark is an "Apple Store" if this Trademark were used with a fruit stand which primarily sold apples. This is a weak Trademark because the Trademark "Apple Store" names or closely describes the goods: apples. Moreover, a Trademark such as the"Red Apple Store" would only be slightly stronger and enforceable because the word "Red" actually describes the apples in to be sold. The underlying principle of Trademark Law is to prevent businesses and individuals from monopolizing general words which would prevent others from naming or describing the goods which are to be sold.
An example of a strong Trademark would be Apple® Computer. Apple® Computer is a very strong Trademark because of the unlikely juxtaposition between high-tech gizmo with gigabytes, software, and geek-speak and fruits. This unlikely combination between the word "apple" and the good it is to brand (computer) makes the Apple® Trademark strong.
What are the benefits of having a strong Trademark as opposed to a weak Trademark? In the previous example, let's assume that "Apple Store" is given some Trademark status with respect to a street-side apple cart in a farmer’s market. Because the "Apple Store" Trademark is a weak Trademark, a competitor may compete under the Trademark "Red Apples Store" and would likely not be in violation of a Trademark infringement dispute. Generally speaking, the weaker the Trademark, the closer a competitor can come to it without creating actual infringement.
Regarding the Apple® Computer Trademark, a competitor would be liable for trademark infringement if they were to market computers as Green Apple Computers. Because the Apple® Trademark is strong, Trademark Law will not allow businesses from using a Trademark on computers and attendant products and services which even remotely resemble their Trademark.
Businesses are in a stronger legal position as it concerns Trademark Law to create Trademarks which do not name, describe, or imply the goods or services with which they desire to use the trademark.