What is the Principal Register?
Under the federal trademark registration scheme, there are two different trademark registers. One is the Principal Register and the other is the Supplemental Register. One of the requirements for a trademark registration is that the mark must be distinctive. Some trademarks are inherently distinctive, and these marks can be registered on the Principal Register as soon as a trademark application has worked through the application process. When a mark is placed on the Principal Register, the trademark owner is granted exclusive rights in the mark.
Marks which are capable of being protected but which are not inherently distinctive (principally descriptive marks) cannot be registered on the Principal Register until the trademark owner can show that the mark has acquired secondary meaning - that is, that the mark has acquired the requisite distinctiveness. Marks like this, that cannot be placed on the Principal Register because they are not inherently distinctive but which otherwise meet the qualifications for registration, can instead be placed on the Supplemental Register. This does not offer many benefits to a trademark owner, however, aside from allowing the owner to bring a federal court action in the event of any infringement - the owner does not get the exclusive rights granted by having a trademark on the Principal Register.