A cisterna (plural cisternae) comprises a flattened membrane disk which makes up the Golgi apparatus. A typical Golgi has anywhere from 3 to 7 cisternae stacked upon each other like a stack of dinner plates. The cisternae carry Golgi enzymes to help modify cargo proteins traveling through them destined for other parts of the cell.
The cisternae also carry structural proteins important for its maintenance as a flattened membrane and its stacking upon each other.
The earliest cisternae are called the cis-cisternae, followed by the medial cisternae, then the trans-cisternae (as they move away from the endoplasmic reticulum).
The formation of new cisternae is often called the cis-Golgi network and at the end of the Golgi where transport to other parts of the cell occurs is called the trans-Golgi network. Both are thought to be specialized cisternae leading in and out of the Golgi apparatus.