Think "brand" and trademarks are not far behind. However, brand is not a legal term with legally defined rights attached.
Trademarks are the "things" that customers come to associate with a specific company. That "thing" could be a name, logo, the sound of particular musical notes, a color, a package design, etc. As long as the "thing" is capable of reminding or suggesting to the customer that they are dealing with a particular source of services or goods, that "thing" can have trademark legal rights attached to it. Trademarks are considered assets of a business, and thus can be sold, licensed or even mortgaged as collateral.
Legal Rights Given Trademarks
The primary legal right given to a trademark owner is the right to stop all other related businesses from using the same name, logo, etc. in a manner that might cause consumer confusion. For this reason, practitioners will sometime refer to trademarks as "source-identifiers." Famous trademarks receive vastly greater rights than non-famous trademarks. The enhanced rights nearly amount to a monopoly in the "thing" used as a trademark, except for limited fair use or parody exceptions.
What a trademark does for consumers:
Trademark law is rooted in consumer-protection. This is important to keep in mind, since this will often become the basis of a judges decision one way or the other when it comes to enforcing one company's trademark over another company's. Trademarks allow individuals to be better consumers. The law is there to ensure that consumers can repeat their positive buying experiences by searching out familiar brand names, and avoid bad buying experiences by steering clear of brands they didn't like.