What is Compulsion?

Legal Definition
The forcible inducement to au act.

2. Compulsion may be lawful or unlawful. 1. When a man is compelled by lawful authority to do that which be ought to do, that compulsion does not affect the validity of theact; as for example, when a court of competent jurisdiction compels a party to execute a deed, under the pain of attachment for contempt, the grantor cannot object to it on the ground of compulsion. 2. But if the court compelled a party to do an act forbidden by law, or not having jurisdiction over the parties or the subject-matter, the act done by such compulsion would be void. Bowy. Mod. C. L. 305.

3. Compulsion is never presumed. Coercion. (q. v.)
-- Bouviers Law Dictionary
Legal Definition
Constraint; objective necessity. Forcible Inducement to the commission of an act Navigation Co. v. Brown, 100 Pa. 346; In S. v. Kimball (O. Ct) 117 Fed. 163; Gates v. Hester, 81 Ala. 357, 1 South. 848.
-- Black's Law Dictionary
Legal Definition
Impelling one to do an act by physical or moral force.
-- Ballentine's Law Dictionary