First Two Layers
First Two Layers, or F2L are normally the first two bottom layers of the 3x3x3 cube, or essentially all layers up until the last layer on larger cubes.
The definition is a little diffrent depending on the subject or who you are talking to. Normally it is as above but it may also refer to the part of the Fridrich method that solves the pairs witout counting the cross part.
There are many ways to solve the 'F2L' on a cube. A common system is using the Fridrich method first two layer approach. After solving the cross, a corner-edge pair is paired up, and then inserted into the correct slot. A total of four corner edge (or 'CE') pairs are made and inserted to solve the first two layers.
Another way to solve the 'F2L' is by building blocks, common during the first two layers of the Petrus method.