"Bumping the lamp" is a term used by Disney animators (and probably people from other animation studios as well) that refers to small details painstakingly added into a film scene to make it perfect, even if the chance of many people noticing it is slim. The term is named after a scene in Who Framed Roger Rabbit in which live action actors continually bump into a hanging lamp while trying to get Roger (a cartoon character) to settle down.
The scene originally did not contain realistic lighting effects on Roger, but they were added as one of the final changes to the film before release. This is allegedly because the animators at Disney (whose characters are used in the movie) noticed the slight gaffe and pointed out the lack of attention to detail. The director Robert Zemeckis, famous for his diligence in special effects perfection, might have had something to do with it as well. The story is only partially told in the movie's special edition DVD bonus features.
While it's clearly not one of the most entrenched and widespread of industry terms, Disney claims that "bumping the lamp" is a huge part of their company ethos. While the vast majority of people would never notice something as minor as the lamp-bumping in Roger Rabbit, the few people who do animation for a living, or are just generally perceptive, will notice and the suspension of disbelief will be shattered. This company attitude of "doing things right" is, according to Disney, part of what makes their employees enjoy coming into work each day, because they take pride in doing stuff well for the sake of it. How much of this is genuine and how much is corporate posturing is left as an exercise for the reader.