Sigma

Sigma is a letter of the Greek alphabet which is often used in maths, science and technology. It stands for 'sum' which means 'adding up', so it's often used to describe the process of adding up a bunch of numbers. For example, if you have a list of numbers like 1, 2, 3, 4 and 5, the sigma would mean that you have to add them all together to get the answer 15.