The fundamental object in String Theory, which replaces the notion of a particle in standard Quantum Mechanics. Rather than being a simple point-like object, fundamental particles become tiny strings or loops. The vibrations of these strings result in various properties like spin.
Come, you lost Atoms, to your Centre draw,
And be the Eternal Mirror that you saw:
Rays that have wander'd into Darkness wide,
Return and back into your Sun subside.
From Farid al-Din Attar's
The Conference of the Birds