A trademark is a word, phrase, design, or other feature that primarily serves to identify the source of a product or service (a mark that identifies a service may also be called a service mark). Drawing from the principle that consumers have a right to know the source of the things that they buy, most governments have created legal protections for trademarks, allowing the owner of the mark to take legal action against another party that uses a mark without permission. As international trade has increased, countries have entered into various treaties which make it easier for a mark in use in one country to gain protection in others.
Along with patents and copyrights, trademarks represent one of the three primary areas of intellectual property law. The primary differences between trademark and other intellectual property regimes lie in the duration and the scope of what may be protected. While both patents and copyrights issue for a specific, limited time, trademarks can persist without end, so long as the mark is used to identify the goods for which it has been registered, or with which it is used.
Barriers to use of a mark
In every system that permits the registration of trademarks, some determination must be made as to whether a proposed mark is registrable. The first inquiry into the registrability of a mark is whether the mark is strong enough to receive protection. Other considerations are also addressed, such as the potential of the mark to mislead or offend. Once the registrability of the mark is otherwise determined, the mark is examined to determine the likelihood of confusion with an existing mark.
Classification of marks by strength
Marks are generally classified as being generic, descriptive, suggestive, arbitrary, or fanciful, although different systems may use different terminology to describe these classes.
A generic mark, which is merely the name of the product itself, can not receive protection because all competitors must be given the right to describe their goods. A common example is the word "apple". A seller of apples could not use the word "apple" as a trademark, because that seller would then be able to prevent all others from using the word to describe their products. However, nothing prevents a seller of computers from using the name Apple for a brand of computers, as no other seller of computers needs to use the word apple to describe their products. Occasionally, a mark becomes so widely used to designate a type of product (rather than identifying the product with its produce) that the mark becomes generic. Famous examples of registered marks that became generic include escalator and aspirin.
A descriptive mark does not identify the product itself, but rather a characteristic of the product. There are several special categories of terms that are deemed descriptive. Laudatory terms, such as "great" or "best" are generally not registrable as marks. Similarly, geographic terms are considered descriptive, and in some countries are unregistrable under any circumstances. A geographic term that does not correctly identify the source of the product may be deemed "misdescriptive", and denied registration on the basis that it misleads consumers into thinking that a product comes from a region with a reputation for providing quality versions of such a product. Many countries, particularly in Europe, have entered treaties which prevent the misdescriptive use of famous regional names (such as Champagne and Burgundy).
Descriptive marks may become eligible for registration in some jurisdictions if the owner of the mark can demonstrate that extensive use of the mark has led consumers to identify the term with the owner's particular brand. This is referred to as developing "secondary meaning". For example, Kentucky Fried Chicken describes the cuisine of a particular locality, but the phrase is now entirely associated with a particular restuarant chain.
The remaining classes of marks receive much stronger protection. A suggestive mark hints at the product, but is sufficiently abstract to avoid describing it. Classic examples of a suggestive marks include "Coppertone" for tanning oil, "MicroSoft" for computer software, or "Tropicana" for orange juice. Commentators have frequently noted the suggestive marks are often the best marks, leading consumers to quickly and easily identify the mark with the product. An arbitrary mark is a term completely unrelated to the product, such "Apple" for computers, "Pledge" for furniture polish, "Fossil" for watches, or "Civic" for an automobile. Finally, a fanciful mark is a completely made-up word, such as "Acura" or "Viagra". Arbitrary and fanciful marks receive the strongest trademark protection, because it is very easy for competitors to avoid accidentally adopting marks that are similar, or using those terms in describing their own products.
Likelihood of confusion
A party may not use or register a trademark that is likely to cause confusion with an existing mark owned by another party. In determining whether confusion may occur, courts and administrative bodies consider both the mark itself and the goods or services to which it is applied. In some instances, identical marks are permissible where they are used on completely unrelated goods or services. For example, the marks of Ace bandages and Ace hardware stores have not led to conflict, nor has the sale of a soap called Dove caused confusion with Dove chocolate bars.
When Toyota launched the Lexus line of luxury vehicles in 1987, Mead Data Central, which owns the Lexis legal research service, sued for trademark infringement on the theory that its upscale consumers (like lawyers) would confuse Lexus with Lexis. Mead lost on appeal in 1989 when the Court of Appeals for the Second Circuit held that there was little chance of consumer confusion. 
Other factors that are commonly considered in weighing possible confusion include the strength of the mark, the level of sophistication of consumers of the respective goods and services, and the channels of marketing and trade in which the products travel. Although a party claiming infringement of its mark need not demonstrate instances of actual confusion, such a showing is considered very strong evidence of a general likelihood of confusion. Similarly, a showing of intent to cause confusion by the other party will be considered strong evidence that confusion is likely to result.
Where two or more identical marks are in use in geographically distinct areas, the respective owners of those marks may each be entitled to the use of the mark in their geographic region, and may bar other users from entering that region. In the United States, if certain conditions are met, each user may be entitled to a concurrent use registration, providing each mark with the benefits of federal trademark registration.
Other registrability considerations
Although surnames are generally arbitrary with respect to products, a surname will usually be unregistrable based on the principal that any persons sharing that name should have the right to use their own name in connection with products that they produce or sell. Like a descriptive term, a surname can be registered if it has developed a secondary meaning, as with "Disney" for example.
Another barrier to registration in the United States is the tendency of a mark to offend, because it constitutes vulgarity or is disparaging towards a person or a group.
- Mead Data Central v. Toyota, 875 F.2d 1026 (2d Cir. 1989)