A more thorough explanation:

Vicarious reduction to practice is a legal doctrine that allows one party to claim credit for another party's actual reduction to practice of an invention. This means that if one party can prove they came up with an invention first, they can still get credit for it even if someone else actually made it.

For example, let's say that John and Jane both come up with an idea for a new type of phone. John files a patent application for the idea, but Jane actually builds a working prototype of the phone. Even though John didn't physically make the phone, he can still claim credit for it because of vicarious reduction to practice.

This doctrine is important in patent law because it helps determine who gets credit for an invention. The date of reduction to practice is critical in determining priority between inventors competing for a patent on the same invention.