Generally, trademarks exists to identify particular sources of goods or services and allow their owners to prevent others from using them to confuse the public as to the source of the goods or services. However, there are circumstances when it’s ok to use others’ trademarks – these circumstances are called “fair use.”
Fair use is an exception to trademark infringement. It generally arises in two circumstances: (1) when a trademark is used in its ordinary descriptive sense to describe a product or service (called “descriptive” fair use); and (2) using the trademark to refer to the trademark owner’s and the actual goods and services associated with the mark (called “nominative” fair use).