While the term "service mark" refers to marks used in selling services, "trademark" can be used to refer either to marks selling goods, or as a general word meaning any kind of source identification symbol, such as a certification mark, collective mark, service mark or trademark.

Certification marks are used to signify a certain level of quality, or that specific standards have been met, while Collective marks are used to identify associations of companies or organizations.

Any mark, whether a service mark, trademark, collective mark,  or certification mark, can be made up of a symbol, word, phrase, smell, sound, or even packaging design.  The only requirement to qualify for use as a trademark is that the "thing" must be used to distinguish its own brand of goods or services from other brands.