A canard is a forewing, an aerodynamic part which is placed ahead (or fore) of a craft's “main” wing which generates less lift than the main. It is useful for planes as it will tend to stall sooner than the main wing as pitch, thus the angle-of-attack, increases. This shifts the center of lift backwards into a more level and stable flight orientation.
Since version 1.0, all parts generate lift, so a canard can in theory be any part. However, smaller wings are best used for static canards. There can be complex interactions between static canards and likewise static main wings can lead to issues with stability in aerodynamic stalls. Active canards made with control surfaces, and in particular controlled wings like the AV-R8 Winglet and the Advanced and the Standard Canard, can actually increase maneuverability and stall performance.
- → See also: Canard article on Wikipedia