What does h.264 mean on a DVR?

H.264 - how the DVR squashes information into a smaller space

Left un-compressed, raw footage coming into a DVR from the cameras would soon fill up the hard drive. To get around the problem programs called codecs have been developed to compress the data so it takes up less space. The most common codec used in DVRs is H.264

Compression codecs are very common. JPEG is a well-known compression method used in still images. H.264 was developed by 2 organisations and is also known as MPEG-4 AVC. H.264 is most commonly used in Blu-ray discs and streaming videos such as Vimeo, YouTube and iTunes.