A fiber is a particularly lightweight kernel thread scheduler dependent thread of execution using co-operative multitasking.
A fiber is a particularly lightweight thread of execution.
Like threads, fibers share address space. However, fibers use co-operative multitasking while threads use pre-emptive multitasking. Threads often depend on the kernel's thread scheduler to preempt a busy thread and resume another thread; fibers yield themselves to run another fiber while executing.
node-fiber introduces Fiber support for v8 and Node JS
Source: Wikipedia