This refers to a basic RWD/Mobile optimized site. It is used when the budget doesn’t allow for extensive definition and design of a mobile website. For example, an RWD typically has 4 breakpoints, one for a mobile phone, another for a tablet, another for a small desktop and one for a large desktop. To minimize costs only one design e.g. mobile phone is created and the other devices are implemented as the developer thinks best. In other words, a RWD Starter website is an entry level mobile site where not every type of design or functional feature is fully defined and designed before it is developed and released for review.
Make sure you understand to what extent your Mobile site is designed and defined. Also keep in mind that designing and defining all aspects of a Mobile site takes a considerable amount of time and may be cost prohibitive.