Pre-registration is an exclusive offering that allows interested registrants the ability to submit their domain name order prior to the General Availability period. Pre-registration is a favored way to get domain registrations because it leverages industry leading technology to register a domain name in the early moments of availability when contention is the highest.
Using Pre-registration does not guarantee the domain will be registered to you, only that it will be ready and queued up to go for the opening of the General Availability period.