What is a Schottky Diode?
Ordinary semiconductor diodes are a junction of N and P semiconductor material.  It turns out you can make a diode from what is sort of half of a semiconductor junction.

Schottky diodes are a junction with one side a P or N semiconductor, but the other side just metal.  The result still functions like a diode, but has the following differences relative to circuit design:

The forward drop is about half.  This is very useful in high current applications since the diode will dissipate less power.  It also helps with efficiency in switching power supply applications.

The reverse leakage is significantly higher, especially at high temperatures.  This is something you have to watch out for and design for accordingly.  Take a look at the datasheet of an ordinary Schottky diode, like 1N5818.  You may be surprised how much it can leak backwards, especially at high temperature.

The reverse recovery time is much faster, essentially instantaneous for most applications.  This is very useful in switching power supplies that run in continuous mode.  In that case, there is forward current thru the diode when the switch is turned on, reverse biasing the diode.  Silicon diodes can be a problem in this application because for the first few 10s or 100s of ns the switch is essentially shorted by the diode still conducting even though it is reverse biased.  This leads to inefficiency and a lot of stress on both the switch and the diode.

Schottky diodes are not available with as high reverse voltages as silicon diodes are.  Above about 100 V they get difficult to find or expensive when you do.