HDrip is a rip of a HD broadcast
The term hdrip is mainly shown on forums or download sites that offer illegal content. When a file is a HDrip, you can assume that it is a pretty good quality, because it is High Definition.
Someone has thus stopped a DVD movie in his computer and converted the movie as 1 file into a certain video format (often XviD or DivX). This has the effect that your movie is only about 750MB large, and no more 4gb. Most people will not see/hear the quality loss. In The illegal circuit there is often a distinction between a cam version and a DVD-RIP.