A movement that began to gain prominence in the 1960s, deconstructionism was a school of literary critics that included thinkers like Jacques Derrida and da man, Paul de Man. Deconstructionists were very interested in questioning the certainty and stability of texts. Texts won't always mean the same thing because language, they pointed out, relies on context and is, therefore, incredibly unstable.
See, before deconstruction came along, there were these guys called the Structuralists, who believed that everything is defined by what it is not—its opposite. So hot is not cold, good is not evil, man is not woman. But deconstructionists pooh-poohed this idea, believing that they set up unfair power structures in Western culture—power structures that favored men over women, whites over people of color, etc.
But before you go thinking that Deconstructionists were all about merely reversing these oppositions, remember their name. They didn't want to reverse them; they wanted to deconstruct them altogether, to show folks that this way of looking at the world was, well, stupid and dangerous. Deconstructionists believe these oppositions are actually contradictions, and harmful ones at that. Men aren't the opposite of women at all. Good is not the absence of evil, no siree. And if we live our lives thinking that, we're allowing unfair power structures to create meaning in our lives and literature. Or at least, so the deconstructionists say.