Beta-level simulations were sophisticated computer programs designed to mimic a person in appearance, mannerisms, and thought-patterns. While capable of successfully impersonating a human mind down to their most minute idiosyncrasies, they were not in fact self-aware -- they were just near-perfect imitations of life. As such, they enjoyed no legal rights or protections.
In Yellowstone society, and presumably other Demarchies, it was considered a most egregious social faux pas to allow someone to believe a beta-level simulation was in fact alpha-level; however, mistaking someone for their beta-level was itself an insult, as Ilia Volyova finds out when excoriating a customs official for Yellowstone.
RS Glossary entry
Beta-level: A simulation of an actual individual created by mimetic software. Turing compliant, but enjoys little or no legal protection under most authorities.
- description from the official RS glossary 
List of beta-levels
- Those made based on Calvin Sylveste's life before Dan Sylveste left for Resurgam with them in his possession; multiple copies, only one active in an escritoire at a time.
- The warchivist on the Nostalgia for Infinity.
- Revelation Space universe - RS Glossary - B, AlastairReynolds.com, the official website of Alastair Reynolds