Context means all the stuff that is not included in your work, but influences it all the same.
For example: when an architect designs a building, the context of his work may be the surrounding landscape, the type of soil, and so on. The given budget and costumer preferences would also be part of the context.
Similarly, the context of a single panel in a comics book would the layout of the page, the artistic style of the book, the story, and also the set of panels surrounding it.
Always make sure you’re asking yourself context-revealing questions. How is your work going fit in? How does it connect or contrast with everything around it? What’s the style of the context, and how do you keep your work consistent with it? What is the context trying to achieve, and how can your work contribute? And, perhaps the most telling question of all: what would be missing in the big picture, if your work had been omitted?