I've always heard that it was a distinct fighting style that used two men where one covered the other's with the shield while the man with the weapon attacked. For example, men with shields protecting commanders.

The term can also apply to soldiers with large shields protecting a unit's flank, like the right side of a phalanx or archers.

Or the term can apply to a servant that carries shields on the march or into battle.

The one mentioned in Samuel was probably the first sort or the last sort especially if the shield was huge.