A surd is a mathematical expression, employed by schools simply because it sounds a bit like turd and you should always call a spade a spade, or something that at least sounds similar. Surds currently hold the record for highest number of learning related injuries. This year figures hit an astonishing 20 million students worldwide. The most injuries occur in students just prior to their exams. The public has been advised by the UN department responsible for this sort of thing to keep exposure to surds a minimum.