A "fiber" could be a specific state in an async state machine (e.g. a Node.js program) or a distinct stack on a M:N threads mapping (e.g. a Go program). Either

A "fiber" could be a specific state in an async state machine (e.g. a Node.js program) or a distinct stack on a M:N threads mapping (e.g. a Go program). Either is far lighter weight than an OS thread. What userspace fibers are you referring to? I don't have experience with Python, Ruby, or Lua, but IIRC Python has an async mode not unlike Node.js.