What is "contraband of war"

Contraband \Con"tra*band\, n. [It. contrabando; contra + bando ban, proclamation: cf. F. contrebande. See Ban an edict.]

1. Illegal or prohibited traffic.

   Persons the most bound in duty to prevent contraband, and the most interested in the seizures.
   --Burke.

2. Goods or merchandise the importation or exportation of which is forbidden.

3. A negro slave, during the Civil War, escaped to, or was brought within, the Union lines. Such slave was considered contraband of war. [U.S.]

   Contraband of war, that which, according to international law, cannot be supplied to a hostile belligerent except at the risk of seizure and condemnation by the aggrieved belligerent.
   --Wharton.