This is the release group. In the "warez scene," groups build reputations. (often stylized as ROVERS) were prominent in the early 2010s for releasing high-quality TV rips. Unlike "web-dl" groups that rip from iTunes or Amazon, Rovers specialized in Bluray encodes . Their tag implies a guarantee: proper cropping, correct aspect ratios, chapter markers, and preservation of original audio tracks.
This is the source. Why does this matter? Streaming services compress video to save bandwidth. A Bluray source is untouched, direct-from-disc media. The colors are richer (specifically the deep greens of Starling City), the black levels are deeper (essential for a show that takes place mostly at night), and the audio is lossless. The combination ensures you are watching the show exactly as the directors intended before bandwidth throttling.
: This indicates the source material . The file was "ripped" directly from the official physical Blu-ray discs, which provides the highest possible baseline for video and audio quality compared to TV broadcasts or streaming captures.