Final Answer:
An intramuscular injection targeting the deltoid is administered in the deltoid muscle.
Step-by-step explanation:
The deltoid muscle is a triangular-shaped muscle located on the shoulder. It is a common site for intramuscular injections, particularly for vaccines and certain medications. To administer an injection in the deltoid muscle, the healthcare professional locates the acromion process (the bony prominence on the shoulder) and injects into the thickest, central portion of the deltoid muscle below this point. This muscle is chosen for its accessibility and relatively low risk of hitting underlying nerves or blood vessels. The deltoid muscle is commonly used for vaccinations, such as the influenza vaccine, and other medications requiring an intramuscular route of administration.