A trademark is, broadly speaking, any mark that is used for indicating goods or services in commerce. Usually, it is necessary to register the mark with a local trademark office before it gains protection under trademark law. The exact rules differ from country to country, and sometimes you also have some kind of protection without registering the mark first. A trademark holder can forbid others from offering particular goods or services using the trademark or a confusingly similar sign. It is also often possible to act against use of the trademark which dilutes its reputation.
A trademark can be one or more words or an image (a logo). Sounds and colors can sometimes also be used, but this is more difficult and may not be permitted in all countries. To indicate that a word, phrase or image is a trademark, the suffix TM can be used. Note that this indicator has no legal status in countries where only registered trademarks are protected against use by others. A registered trademark is indicated with the ® symbol.