Pigtails, the connector is a mechanical or optical device that provides a demountable connection between two fibers or a fiber and a source or detector. Much about the tech jargon, in simple words fiber optics pigtail is a piece of fiber optic cable with only one fiber optic connector on one side of the cable. As with fiber optic communication, fiber optic pigtails are also single mode and multimode, quite obvious, with different types of termination/connector as SC, LC, ST etc.