Force kick
From Wookieepedia, the Star Wars wiki.
The term "Force kick" jokingly refers to a particularly badly-choreographed and -shot fight sequence within the "Skirmish at Carkoon" scene of Return of the Jedi in which Mark Hamill/Luke Skywalker kicks one of Jabba the Hutt's henchmen in the head, causing him to fall into the sarlacc pit while Boba Fett is flying helplessly by in the background.
The choreography flaw consists in the stuntman reacting to the impact of the kick too late when Hamill is already lowering his leg, while the shooting flaw consists in the camera being placed such that it is very obvious that the kick does not actually hit the stuntman.
The sequence is referred to as the "Force kick", which jokingly speculates that Luke uses Force telekinesis to make the henchman fall into the sarlacc pit rather than the physical impact of the kick. Of course, it is never suggested that the Force kick is an actual Force power in the Star Wars universe, and a retcon of the sequence along those lines is highly improbable.
A similar blooper happens in Episode III during the Mustafar fight scene. When Vader dropkicks Obi-Wan Kenobi on the tabletop, his feet clearly do not connect with Kenobi. Coincidentally, another Force kick occurs in Willow, when Madmartigan kicks one of Bavmorda's soldiers in Tir Asleen castle.
The Force kick sequence sparked off a minor fad within the Star Wars-oriented part of the YTMND community, in which the term might have originated.
[edit] The "Force kick" sequence
 The kick is at its peak and would, in reality, have impacted on the kicked person. Notice the space between Hamill's foot and the stuntman. |
 Hamill lowering his leg, only now does the stuntman react to the kick. |
 The flawed action sequence is not always noticed, as focus is on Boba Fett's movement in the background. |
 Hamill's foot back on the ground, the stuntman turns to fall into the sarlacc. |
