Relevance simply means that the information, citations and argument embedded in your essay must directly relate to the essay title, either answering specific questions or broadening specific areas of discussion. Just listing information is never relevant in a computing science essay. You must use the information to illustrate and strengthen the point you are trying to make.
It's important to be clear about relevance because irrelevance guarantees poor marks. Luckily, keeping your essay relevant is easy: just keep asking yourself two key questions:
1. Does this piece of information/quote/argument relate directly to the essay title?
2. Does this piece of information/quote/argument add weight to my response?