A BDRip is a multimedia file that contains content that was sourced from a Blu-ray Disc product. As the "rip" part of the name applies, the copy is generally not a 1:1 copy, but instead is usually re-encoded. Most of the time Blu-ray disc rips (BDRips) contain AVC video that has a lower bitrate to the original content. Sometimes the creator of a BDRip may choose to lower the video resolution from Full HD 1080p content to 720p. The most common multimedia container used for BDRips is the Matroska (MKV) container, which would be used for its suitability.
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.
BDRips are widely found on the Internet, posted by pirates and labeled as either BDRip or "BluRay". Playing BDRip content depends on the resources you have available in your computer.
More information: How to play MKV files