What is the difference between an isolation transformer and an autotransformer?

Whether an isolation transformer or an autotransformer, a transformer typically steps the supply or line voltage coming into the unit up or down to whatever voltage the load or downstream component or circuit requires. While sometimes confused, there is a critical difference between the isolation transformer and the autotransformer:

By definition, the input and output windings of an isolation transformer are separate windings—physically isolated and electrically insulated from each other by distance, an insulation barrier, or both.

An autotransformer, on the other hand, is uniquely designed to accommodate the range of both the available input and required output voltages in a single winding. And because the “common” section of that single winding is shared between the input and output of the unit, there is no physical isolation or electrical insulation between them.