original_query: What is Proto-Balto-Slavic (PBS or PBSl)?
query: What is Proto-Balto-Slavic (PBS or PBSl)?
answer: Proto-Balto-Slavic is a reconstructed hypothetical proto-language that descended from Proto-Indo-European.  Balto-Slavic languages, including Lithuanian, Polish, Russian, and Serbo-Croatian, are thought to have developed from it.