Context means the setting of a word or event. If your friend is furious at you for calling her your worst enemy, remind her that the context of those remarks was Opposite Day.
Context comes from the Latin for how something is made. It was first used to talk about writing, as in "the beautiful phrase occurs in the context of the concluding paragraph." We use it now to talk about any circumstance in which something happens. You might say that you can't understand what happens without looking at the context. When someone takes your words but makes it sound like you meant something else, they've taken your words out of context.