Definition
Wing or tail surfaces made up of more than one separate aerodynamic section working together, such as a main wing combined with leading-edge slats and/or trailing-edge flaps that extend away from the wing to form distinct elements with airflow passing between them.
Plain English
A wing built from several separate pieces that move out and work together, instead of one solid shape. The slats at the front and the flaps at the back become their own little wings, with gaps of air flowing between them.
Context Anchor
Seen in icing discussions when the handbook explains how ice can affect wings or control surfaces that have gaps, flaps, or movable front-edge sections.
Derivation
Multi means many. Element here means a separate part of a system. So a multi-element airfoil is simply a lifting surface built from several distinct aerodynamic parts rather than a single shape.
Why Pilots Care
Ice forming on the gaps and surfaces of these airfoils sharply reduces lift and raises stall speed, increasing risk during approach and landing in instrument conditions.
Intuition Check
Do not read element as a chemical element here. In this term, an element is one separate airfoil section that works with the other sections.
Example Sentence 1
With the flaps and slats extended on approach, the wing becomes a multi-element airfoil, and even a thin layer of ice can noticeably degrade its performance.
Example Sentence 2
Extending the multi-element airfoils allowed the aircraft to maintain lift at the reduced speed required for landing.