Quote out of Wikipedia. Hope this clarifies your question :
"In traditional Japanese, it is an abbreviation of the Japanese gairaigo computer graphics (コンピュータグラフィックス?), used to refer to any form of digital artwork, from digitally shaded dōjinshi to legitimate cinematic art (like Toy Story). In the West, however, the term has come to refer exclusively to 2D digital art, as the term computer-generated imagery (CGI) is used to describe art forms that CG otherwise describes. In recent years, the hentai industry has begun to incorporate this into their market schemes."