The EB-3 visa means it is the third preference employment-based (EB) green card. As with other green cards, it gives the holder indefinite/permanent residency to live and work in the United States.
EB-3 visa requirements are somewhat less stringent than the first and second preference employment-based alternatives (i.e. EB-1 and EB-2). Around forty thousand EB-3 visas are currently awarded each year.
The employer will have to go through the PERM labor certification process under the EB-3 Visa requirements, as with other employment-based visas!