The Internet is a global system of interconnected computer networks that connect billions of devices worldwide using TCP/IP. It allows fast and cheap access to information and online purchasing. However, there are also disadvantages like security threats from viruses, fraud, pornography, and inaccurate information. The document discusses the definition of the Internet, its advantages such as speed, low cost, and access to information and goods, and disadvantages including viruses, fraud, inappropriate content, and potential for incorrect facts.