This gives you a non-exclusive, royalty free, worldwide, irrevocable, perpetual license to use the design in your business. The logo will remain for sale on 99designs for others to potentially buy, customize, and use.
This buys you the FULL intellectual property rights to the design from the designer. You get to own the design exclusively. If you choose exclusivity, the logo will be removed instantly from the store, but only the first buyer has this option.