Clarity refers to how many inclusions, or spots and flaws, are in a stone. Generally speaking, fewer inclusions means a more valuable diamond, but flaws don't necessarily reduce a diamond's beauty, especially if they can’t be seen by the naked eye.
The majority of diamonds do contain some flaws, most are inclusions of other minerals, created during crystal growth.
The system for clarity grading established and implemented by the Gemological Institute of America (GIA) is accepted by all diamond trading centers as the standard for diamond grading. It assesses diamond clarity according to size, position, color, and number of inclusions or flaws present.