A trademark (also written trade mark or trade-mark) is a form of intellectual property that consists of a word, phrase, symbol, design, or a combination that identifies a product or service from a particular source and distinguishes it from others. Trademarks can also extend to non-traditional marks like drawings, symbols, 3D shapes like product designs or packaging, sounds, scents, or specific colours used to create a unique identity. For example, Pepsi® is a registered trademark associated with soft drinks, and the distinctive shape of the Coca-Cola® bottle is a registered trademark protecting Coca-Cola's packaging design.

The primary function of a trademark is to identify the source of goods or services and prevent consumers from confusing them with those from other sources. Legal protection for trademarks is typically secured through registration with governmental agencies, such as the United States Patent and Trademark Office (USPTO) or the European Union Intellectual Property Office (EUIPO). Registration provides the owner certain exclusive rights and provides legal remedies against unauthorised use by others.

Trademark laws vary by jurisdiction but generally allow owners to enforce their rights against infringement, dilution, or unfair competition. International agreements, such as the Paris Convention and the Madrid Protocol, simplify the registration and protection of trademarks across multiple countries. Additionally, the TRIPS Agreement sets minimum standards for trademark protection and enforcement that all member countries must follow.

The term trademark can also be spelled trade mark in regions such as the EU, UK, and Australia, and as trade-mark in Canada. Despite the different spellings, all three terms denote the same concept.

In the United States, the Lanham Act defines a trademark as any word, phrase, symbol, design, or combination of these things used to identify goods or services. Trademarks help consumers recognise a brand in the marketplace and distinguish it from competitors. A service mark, also covered under the Lanham Act, is a type of trademark used to identify services rather than goods. The term trademark is used to refer to both trademarks and service marks.

Similarly, the World Intellectual Property Organization (WIPO) defines a trademark as a sign capable of distinguishing the goods or services of one enterprise from those of other enterprises. WIPO administers the Madrid Protocol, which allows trademark owners worldwide to file one application to register their trademark in multiple countries.

Almost anything that identifies the source of goods or services can serve as a trademark. In addition to words, slogans, designs, or combinations of these, trademarks can also include non-traditional marks like sounds, scents, or colours. Under the broad heading of trademarks, there are several specific types commonly encountered, such as trade dress, collective marks, and certification marks:

To maintain distinctiveness, trademarks should function as adjectives, not as nouns or verbs, and be paired with a generic product or service name. They should stand out from the surrounding text using capital letters, bold type, italics, colour, underlining, quotation marks, or a unique stylised format. For example, say "LEGO® toy blocks" instead of "Lego's."