The prefix 'mega' is often used to describe something that is very large or huge. It comes from the Greek word 'megas' which means great. The prefix 'mega' is often used to describe something that is extremely large, such as a megastructure or megacorporation. It can also be used to describe something that is very powerful, such as a megawatt or megaton. In short, the prefix 'mega' is used to describe something that is very large or powerful.