The native file format of WebGraph.
It is a binary format and highly storage efficient.
It is for example what Common Crawl web graph currently dumps to as of 2025, see e.g.: data.commoncrawl.org/projects/hyperlinkgraph/cc-main-2024-25-dec-jan-feb/index.html
TODO meaning of "BV"?
A quick hands-on introduction to the format by Ciro Santilli can be found at: github.com/cirosantilli/cirosantilli.github.io/issues/198