To make a BDRip, you need to copy the main movie of a blu-ray disc to your hard drive, and then re-encode it to reduce size. BDRips are usually Matroska files, with MPEG 4 AVC video, high quality AAC audio, and possibly subtitles and chapters (this type of file is usually called a "DivxHD" file). BDRips always come in HD, aka 1280x720 resolution or above (MKV files in standard definition are not considered BDRips).
BDRips are the next thing after DVDrips (which are always standard def).
The problem is that, while DVDRips use a video format superior to the one the source uses (MPEG 4 ASP vs MPEG 2 of the DVD), which means it's possible to dramatically reduce the size of the rip compared to the original, BDRips use the same video format as Bluray (MPEG 4 AVC in both cases). This means it's not possible to reduce size that much, if you want to preserve the HD resolution and video quality.
Anyway, BDRips are several times better in terms of quality than any DVDrip. BDRips are also bigger in size. They usually come in two resolutions, 720p (4,35GB~6GB in size) and 800p (7,9GB~13GB in size, often called "1080p" vids).
-Friend: I hate DVDrips, we 'd better rent the DVD
-Me: This is a BDRip, and it has better quality than any DVDRip or DVD. Just watch and tell me.
-Friend: Wow, it's in HD!
BDRips often come packed with subtitle streams (usually part of the MKV file) and DTS or AC3 audio. A BDRip could be made to fit onto single layer DVD media (DVD-5), and so would be around 4.3GB in size. Content up to 8GB will need to be burned to a dual-layer DVD disc. Creating BDRips is not as easy as creating DVDRips yet, and encoding AVC content takes considerably longer than MPEG-2 content. Additionally, when working with Blu-ray content, there a lot of data to be worked with. A Blu-ray Disc could contain up to 50GB of data, which would have to be decrypted and copied to the hard disk drive before it could be re-encoded.
2: What? Haven't you heard of BDRip?
1: No? What's that?
2: It's a lot better quality (High Def), but doesn't take the same size as a dvd.
1: Sounds good, perhaps I'll try that next time then.