Boyd’s Bible Dictionary:
(shield). A small shield is meant, and not a target or mark in a modern sense (1 Sam. 17:6). In the margin it is called “gorget,” which was a defensive piece of armor, in the days of chivalry, used to protect the joint or opening between the helmet and cuirass.
Concise Bible Dictionary:
A shield (1 Kings 10:16; 2 Chron. 9:15; 2 Chron. 14:8). In 1 Samuel 17:6 a small spear is probably intended: the RV. has “javelin.” See ARMOR.