What's that ?
The laptop manufacturers developed new technologies involving two graphic cards in an single computer, enabling both high performance and power saving usages. This technology is well supported on Windows but it's still quite experimental with Linux distributions.
We call hybrid graphics a set of two graphic cards with different abilities and power consumptions. It has nothing to see with other technologies like SLI or CrossFire, intended to improve only the computing power of a system without taking care of power consumption.
With nVidia's Optimus, the images are always sent through the integrated Intel card, even when the computations are made on the discrete card. There's no physical switch which could allow the user to "plug" his monitor to the card of his choice. The user can't use the nVidia GPU directly, even on Windows.