A plot point within a story may be said to be forced if a given development occurred because of a sudden change which had no precedent within the tale.
One common form of plot forcing is sporadic, selective stupidity, the condition whereby a normally competent (or brilliant) character suddenly losses all wit so that said character may be bested (this is especially common with villains as can be ascertained from a cursory review of the rogues gallery of the James Bond series) either for character or plot development (or both). For a specific example, consider the absurdist climax of the Marvel film, Guardians of the Galaxy (2014), whereat the film’s primary antagonist, a ruthless galactic warlord named Ronan, is bested because he is distracted for a unbelievably protracted period of time by the protagonist’s ridiculous dancing (this, I assume, was supposed to be funny). The scene made no sense as there was no precedent for such a intelligent and unhesitating character as Ronan to be utterly stunned by nothing more than exaggerated gesticulations, especially for such a long period of time, as such, the plot advancement (Ronan’s defeat) is ‘forced’ (for attempted comedic effect). This is a case where the intended effect of a given scene (comedy) stands in contrast to both the preceding plot development (impending genocide; high drama) and the propensity of the central character (Ronan; a heedless fanatic ill-inclined to distraction).
Another form of plot forcing (and to my knowledge the most common) is precedentless character enhancement, wherein a character encounters a situation where they are hopelessly outmatched but prevail due to no other reason than their own uniqueness, a uniqueness not previously demonstrated or even known to the character in question, which only manifests when a plotline needs to be advanced. This particular kind of plot forcing is characteristic of ‘chosen one’ narratives (such as: Harry Potter, Star Wars, The Matrix, The Wheel of Time, Supernatural and many others) wherein the ‘fate of the world’ (or some variant on the theme) rests solely upon the shoulders of the protagonist whose uniqueness and pivitol role in world events is generally explained via prophecy. Chosen one characters are typically young (I cannot recall any chosen one stories wherein the prophecized hero was elderly) and seemingly inadequate for the task, yet, despite the chosen one’s complete lack of skills they invariably triumph over the chaotic force or forces which threaten their world due to providential selection (selected by a diety or fate, etc). There are so many critiques of this particular trope that little needs to be said about why it should be avoided, so I shall name only one particular and perhaps seemingly counterintuitive problem it engenders: character limitation. In placing the providential/fated selection of a character as the primary driver of the plot (and most, if not all, the arcs within it) there is something of a hardcap which is placed upon character development; firstly, in that there is no reason at the outset for a chosen one protagonist to develop at all because they are already pre-equipped to deal with every challenge that besets them; a example of this that most will be familiar with can be observed in the film Star Wars: The Force Awakens wherein the protagonist, Rey, defeats the antagonist, Ren, in a duel, despite the fact she had never fought in such a fashion before and he had trained since his youth for martial conflict. She wins not because she is more talented, but because she’s ‘chosen,’ thus, she has to win, otherwise she’d have died and the story would be over and so again, the plot is ‘forced.’
A perceptive writer can see the problem immediately, there is no character building required, which will oft incline the author to ‘quick fixes’ in the advancement of their plot and thus also inclines towards the monotone, the predictable, the grey and unthoughtful; to boring characterization and lazy scenarios.
There are many other forms of plot forcing besides chosen one quick fixes and sporadic, selective stupidity, but these are (to my mind) the two most common.