A diamond with a clarity rating of I1 or I2 is considered relatively low-quality, at least in terms of clarity. I2 and I3 are considered grades of "included" by the Gemological Institute of America, which means they contain significant internal imperfections.
The Gemological Institute of America grades diamonds on a clarity scale from "Flawless" on the one end through varying levels of slight inclusion and blemish to "Included" on the low end. "Blemish" refers to a surface imperfection, such as a polish mark, nick or scratch. "Inclusion" is an internal imperfection, such as a cloud or other mineral inside the diamond. The GIA also grades diamonds on carat, color and cut.