What is a key characteristic of an autotransformer?

An autotransformer is characterized by having only one winding, which serves both as the primary and secondary winding. This unique design allows the transformer to efficiently vary voltage levels while requiring less material than a conventional transformer that has separate windings for primary and secondary. The single winding is tap-connected at different points to provide a range of voltage outputs, enabling both step-up and step-down transformations depending on how the taps are utilized. This flexibility in usage is a distinguishing feature of autotransformers, distinguishing them from traditional transformers that have isolated windings.