A more thorough explanation:

A separable controversy is a claim that is separate and independent from the other claims being asserted in a lawsuit. It is most often associated with the statute that permits an entire case to be removed to federal court if one of the claims, being separate and independent from the others, presents a federal question that is within the jurisdiction of the federal courts.

For example, if a person sues a company for breach of contract and also alleges that the company violated federal antitrust laws, the antitrust claim may be considered a separable controversy that could be removed to federal court.

Another example of a separable controversy is a case that requires a definitive determination of the law on the facts alleged for the adjudication of an actual dispute, and not merely a hypothetical, theoretical, or speculative legal issue. This is also known as an actual controversy.

For instance, if a person sues a city for violating their constitutional rights by denying them the right to free speech, this would be an actual controversy that requires a definitive determination of the law on the facts alleged for the adjudication of an actual dispute.