Central:At or near the center.
In anatomy and medicine (as elsewhere), central is the opposite of "peripheral" which means away from the center. The word "peripheral" comes from the Greek "peripheria" ("peri-", around or about + "pherein", to bear, carry).
A central line is an infusion tube that is located in or near the heart (centrally in the circulatory system). A Swan-Ganz cather with its tip, for example, in the right atrium and ventricle of the heart is a central line. On the other hand, a peripheral line is located on the periphery of the circulatory system. An ordinary IV (intravenous) catheter is a peripheral line.