What is the difference between a buck-boost transformer and an autotransformer?

A Buck-Boost transformer is typically a small single-phase low voltage lighting transformer that can be wired as an autotransformer to provide small voltage corrections for single and three phase applications. An autotransformer is a transformer with a direct connection between the primary and secondary and does not act as an isolation transformer. Autotransformers can also include wider classes of products including buck-boost, dedicated three coil distribution style units, motor starting autotransformers and solar grid tie transformers.