An isolation transformer is a transformer with:

An isolation transformer is designed to provide electrical isolation between its primary and secondary windings. The primary and secondary windings are physically separated to prevent direct electrical contact, which helps to protect sensitive equipment from voltage spikes and ground loops. This isolation also reduces the risk of electric shock to users and protects against noise interference, which is particularly important in medical environments where precise instrumentation is required.

The separation between the primary and secondary allows for the transfer of power without a direct electrical connection, ensuring that the system can operate safely without the influence of ground potential differences. The other options involve features that do not specifically define the function and purpose of an isolation transformer. While some isolation transformers might have multiple secondary windings or grounding configurations, it is the physical separation of the windings that is the defining characteristic of an isolation transformer.