Quarantine:
A restraint placed on an operation to protect the public against a health hazard. A ship may be quarantined so that it cannot leave a protected point. During the quarantine period, the Q flag is hoisted.

Quoin:
A wedge-shaped piece of timber used to secure barrels against movement.

Quota:
The quantity of goods that may be imported without restriction during a set period of time.

Quotation:
An offer to sell goods at a stated price and under stated terms.

Quay:
A structure attached toland to which a vessel is moored. See also Pier and Dock.