A more thorough explanation:

Definition: A structure that holds water, usually between two piers, where ships can be loaded, unloaded, repaired, or kept safe. It can also refer to the part of a building where trucks are loaded and unloaded. In English law, it is the enclosure where a criminal defendant is placed during trial.

Examples:

• A cargo ship pulled into the dock to unload its containers.
• The truck backed up to the loading dock to drop off its shipment.
• The defendant stood in the dock during the trial.

The first two examples illustrate the use of a dock as a structure for loading and unloading. The third example shows the use of a dock in English law as the enclosure where a defendant stands during trial.