Low-Drop Voltage Tracker Working
They are quite similar.

I hope you're familiar how a LDO regulator works, so I don't have to explain that here. Remember that a normal LDO consists of a voltage reference, an error amplifier and a pass element (transistor).

A voltage tracker is the same except that it does not contain the voltage reference. Instead you supply the reference voltage externally.

You can think about them as voltage followers with built-in goodies like overcurrent, temperature and short circuit protection.

And to answer the possible follow-up question right away: "Why do I want a voltage tracker instead of just using a cheap opamp as a voltage follower": A voltage tracker has no problems driving capacitive loads which you need in most voltage supply applications. Opamps on the other hand rarely tolerate more than a few hundret picofarads at their output. They aren't suitable to supply voltage for micro-controllers due to the lack to drive bypass capacitors for example. Voltage trackers on the other hand are.