[mkeeter]

In my experience, "linear regulator" refers specifically to voltage regulators which drop from a high voltage to a lower voltage by burning all of the power in between (e.g. the venerable 7805).

They're useful if the voltage drop isn't too large and/or if you need a particularly stable output voltage; contrast them with switching regulators, which are more efficient but have some amount of output ripple.

One design that I worked on used a switching regulator to generate 5V, then linear regulators to generate something like 3.7V and 2.9V for various sensitive analog circuits.