Definition of face palm:
(v) :
Alternative spelling of facepalm. [To bring the palm of one’s hand to one’s face as an expression of mixed humor and disbelief, disgust or shame; for example, when one is caught off-guard with a particularly bad pun.]
(n) :
Alternative spelling of facepalm. [A gesture of bringing one or both palms to the face, with various interpretations including exasperation, chagrin, frustration, embarrassment (one's own or vicarious), etc.]