The span between a least and a greatest. A range states what is possible without saying which is actual.
Old French rangier (to arrange in a row), related to renc/rang (a row, a rank), of Frankish origin from a Germanic root meaning ring; a range was first a row set in order, and only later the span between its two ends.
The span between a least and a greatest, without saying which point along it is actual. The root's row is still present in the shape: a range is a line laid out, and the two ends are its only fixed claims.