Definitions of Clarity Grades:
When you assign a clarity grade, consider the size, number, position, nature, and colour or relief of the various clarity characteristics. Do not try to analyze them separately.
Flawless (FI): Flawless diamonds show no blemishes or inclusions when examined by a skilled grader under 10x magnification.
The following do not disqualify a stone from the flawless category:
An extra facet on the pavilion which cannot be seen face-up.
Naturals totally confined to the girdle, which neither thicken the girdle nor distort its outline.
Internal graining which is not reflective, white, or coloured, and does not significantly affect transparency.
Internally Flawless (IF): IF stones show no inclusions and only insignificant blemishes under 10x magnification. IF stones can be changed to FI grade after minor repolishing.
Very Very Slightly Included (VVS1 and VVS2): VVS diamonds contain minute inclusions that are difficult for even a skilled grader to locate under 10x. In VVS1, they are extremely difficult to see, visible only from the pavilion, or small and shallow enough to be removed by minor repolishing. In VVS2, they are very difficult to see.
Very Slightly Included (VS1 and VS2): VS stones contain minor inclusions ranging from difficult (VS1) to somewhat easy (VS2) for a trained grader to see under 10x. Small included crystals, small feathers, and distinct clouds are typical.
Slightly Included (SI1 and SI2): SI stones contain noticeable inclusions which are easy (SI1) or very easy (SI2) to see under 10x. In some SI2s, inclusions can be seen with the unaided eye when the stone is placed table-down on a white background and viewed through the pavilion.
Imperfect (I1, I2, and I3): I-grade diamonds contain inclusions which are obvious to a trained grader under 10x magnification, can usually be seen face-up with the unaided eye, seriously affect the stone's potential durability, or are so numerous they affect transparency and brilliance.
Clarity Characteristics
Abrasion: tiny chips along facet junctions, producing white fuzzy lines instead of sharp facet edges are called abrasion.
Extra Facet: a facet placed without regard for symmetry and not required by the cutting style.
Natural: part of the original crystal surface remaining on the polished stone.
Nick: a notch near the girdle or a facet edge
Pit: a tiny opening, often looking like a white dot.
Polish Lines: tiny parallel lines left by polishing.
Polish Mark: surface clouding caused by excessive heat, or uneven polished surface resulting from structural irregularities.
Rough Girdle: a grainy or pitted girdle surface, often with nicks.
Scratch: a linear indentation normally seen as a fine white line, curved or straight.
Surface Grading: surface indication of structural irregularity; may resemble faint facet junction lines, or cause a grooved or wavy surface, often cross facet junctions.
Bearding: beardind are the tiny feathers extending in from a bruted girdle (called hairline feathers on a polished girdle)
Bruise: surface crumbling, often accompanied by tiny, root-like feathers.
Cavity: a large or deep opening.
Chip: a small or shallow opening usually on the girdle edge.
Cloud: a hazy or milky area made up of a number of very small inclusions.
Feather: a separation or break due to either cleavage of fracture, often white and feathery in appearance.
Grain Center: a small area of concentrated crystal structure distortion, usually associated with pinpoints (rare).
Included Crystal:  included crystal is a mineral crystal contained in a diamond.
Indented Natural:  indented natural is a natural crystal that penetrates the stone.
Internal Graining: internal indications of irregular crystal growth; may appear milky, like faint lines or streaks, or may be coloured or reflective.
Knot: an included diamond crystal which reaches the surface of a fashioned stone.
Laser Drill Hole: a tiny tube made by a laser; the surface opening may resemble a pit, while the tube usually looks needle-like.
Needle: a long, thin included crystal which looks like a tiny rod.
Pinpoint: a very small inclusion; under 10x, normally seen as a tiny dot, either singly or in groups or strings.
Twinning Wisp: a cloudy area produced by crystal structure distortion, usually associated with twinning planes.