A more thorough explanation:

Definition: Capable of being forced or required to do something, especially to testify in a court of law.

Example: In a criminal trial, the defendant's spouse is usually not a compellable witness for the prosecution.

Explanation: This means that the defendant's spouse cannot be forced to testify against their partner in court. The term "compellable" refers to the ability to be compelled or forced to do something, in this case, to testify. The example illustrates how the term is used in a legal context.