Crash course on trademarks
A trademark is an exclusive right to a particular sign (like a name, a word or a logo). With the exclusive right, the holder can prevent others from using the trademark in commerce. This way, these others cannot label their goods or services with the same (or a similar) sign, which could confuse potential buyers and allow these others to profit from the reputation of the trademark built up by the trademark holder. A trademark thus does not monopolize the word that is trademarked as such; only use in commerce for particular goods and services is not permitted.
Trademarks can take different forms. Words, letters, digits and graphical signs are common types of trademarks, but also the shape or packaging of a product can be a trademark. The most important requirement is that the trademark is distinctive: the trademark must be able to identify the goods or services it protects as originating from a particular undertaking, and thus to distinguish those goods or services from those of other undertakings. This is important in order to ensure that potential buyers are not tricked into buying a product of one company while believing it is a product of another company.
On the Internet, trademarks have become very important when it comes to domain names. While it is possible for two companies to both have trademark rights for the same trademark (for example, in two different countries, or for different goods and services), only one person in the world can hold a particular domain name. Problems can thus easily arrive when multiple persons or companies want to make use of the same domain name.
Additionally, many problems are caused by so-called "cyber squatters" or domain name brokers who register large numbers of domain names with the intent to sell them at a profit to people who want to host a website under those domain names. This has caused many conflicts with trademark holders who did not want to pay large sums of money to get "their" domain name back. But trademarks law has also been used against organizations and private individuals who criticized particular companies using a domain name like McDonaldsSucks.com.