Taper Ratio can be either in planform or thickness, or both. In its simplest terms, it is a decrease from wing root to wingtip in wing Chord or wing thickness.

The second means of changing the planform is by Tapering (decreasing the length of Chord from the root to the tip of the wing). In general, tapering causes a decrease in drag (most effective at high speeds) and an increase in lift. There is also a structural benefit due to a saving in weight of the wing.

Drag is the one of two components of the aerodynamic force. Lift is the other. As the aerodynamic force increases so does lift and drag.

The Aspect Ratio of an aerofoil is the ratio between the length and the average width of the surface. For a wing, the Aspect Ratio is the ratio of wing length to average Chord. Similarly, for a propeller, the Aspect Ratio is the ratio of blade length to average Chord.

An increase in Aspect Ratio with constant velocity will decrease the drag, especially at high Angles of Attack, improving the performance of the wing when in a climbing attitude. Also there is an increase in the length of span, with a corresponding increase in the weight of the wing structure, which means the wing must be heavier to carry the same load.

A decrease in Aspect Ratio (small Aspect Ratio) will give a corresponding increase in drag because Chord now increases so does the wing planform.