In medical use, choking is the blocking of a person's trachea by a foreign object, vomitus, blood or other fluids. Choking is a medical emergency.
The first aid for choking is to call for help using the emergency telephone number, then to clear the obstruction from the airway using abdominal thrusts aka the Heimlich maneuver and/or artificial respiration. Intubation is the advanced medical procedure indicated, which can be performed by paramedics in the field. See airway obstruction.