Final answer:
The upper arm, particularly the deltoid muscle area, is a common site for subcutaneous injections due to its accessibility and reduced risk of complications.
Step-by-step explanation:
A common site for a subcutaneous injection is the upper arm, specifically in the deltoid muscle area. This location is frequently chosen for its ease of access and the smaller likelihood of hitting bone, nerve, or major blood vessels. Vaccines, like the influenza shot, are often administered in this area. The upper arm site is preferred because it is readily accessible, and the subcutaneous tissue provides a suitable layer for the injection of medication or vaccines.