cipher
n.— «The “Emcee Cypher,” also spelled cipher, is a chance for DJs/producers to showcase their skills while simultaneously enticing a group to create a verbal collage. In hip-hop parlance, cipher refers to something like a jam session. Everyone forms a circle and contributes to the creative experience—DJs, dancers, rappers or graffiti writers.» —“Underground hip-hop, literally, at Medusa” by Hector Williams Philadelphia Inquirer (Pa.) Mar. 17, 2006. (source: Double-Tongued Dictionary)