Which of the following describes a 'tourniquet' in the context of intravenous therapy?

In the context of intravenous therapy, the term 'tourniquet' specifically refers to a tool that is used to temporarily restrict blood flow. This is a crucial step in venipuncture, as restricting blood flow causes the veins to become more prominent and easier to access for needle insertion. The application of a tourniquet helps healthcare professionals identify a suitable vein for the IV line or blood draw, increasing the chances of a successful puncture on the first attempt.

The other options do not accurately describe the function of a tourniquet. For instance, a device to administer medication refers to equipment like syringes or infusion pumps, while an IV access line denotes the actual catheter placed in the vein. A method of contrast injection refers to techniques used in imaging studies to introduce contrast media into the bloodstream. Each of these serves a different purpose in patient care and pharmacology but does not relate to the primary function of a tourniquet.