The term 'BIG PART OF A RISK BOARD' can be solved by the four-letter word 'ASIA'. ASIA is the world's largest and most populous continent, covering 8.7% of the Earth's total surface area and comprising 30% of its land area. It is home to 60% of the world's population and is the birthplace of many of the world's major religions, including Buddhism, Christianity, Hinduism, Islam, and Judaism. As such, it is a major part of the Risk board game, which is based on world domination.