Final answer:
Federated Search allows searching across multiple data sources from one interface. Its availability for Classic customer adoption depends on the specific software, but for Salesforce Classic users, it is not available without switching to Lighting Experience.
Step-by-step explanation:
Federated Search is a feature that allows users to search for information across multiple data sources from one single query interface. Whether Federated Search is available for Classic customer adoption depends on the specific software or platform in question. In the context of salesforce.com, for example, Federated Search was introduced as a feature for Lightning Experience users and is not available for Salesforce Classic. Customers using Salesforce Classic would need to switch to the Lightning Experience to take advantage of the Federated Search feature.