A switchback is a situation in which a ladder moves back two rows and changes direction. The attacker is still in control after the switchback. Although it is not always ladder escape, it often can be and is usually a strong play.
The situation prior to a switchback generally looks like this (assume the piece on D1 is in some way connected to the top):
Red makes a switchback as follows:
Now the ladder continues back to the left:
Note here how red was able to connect back to the D1 piece. This is not always possible, but even if it isn't the switchback can be used to create a long line connected to the edge and four rows back from it, a distinct advantage.
A Different Situation
A different kind of switchback can occur on the third row:
If Blue yields the ladder to the second row, then Red can create a switchback as shown above which would continue back and reconnect. If the ladder stays on the third row then Red creates a switchback as follows:
Red's piece on G3 is connected to the bottom. Play continues: