What are shuttle systems in electron transport chain? Please explain in detail.

Literal meaning of shuttle is the entity that transfer anything form one place to another and comes back to that place.In the same way Eletron transport system is also supplied with some shuttle molecule that transfer electron from one complex to another, like ubiquinone (mobile electron transporter). Apart from electron transport system some other process also have some shuttle system, likeGlycerophosphate shuttle and the Malate-Aspartate shuttle.