TCP/IP, which stands for Transmission Control Protocol/Internet Protocol, is a technical standard for how computers communicate with each other over the internet. TCP/IP was established in the 1970s by the US Department of Defense for use on the internet's predecessor. TCP and IP are separate protocols. Individually they aren't very useful, but together they allow very powerful capabilities. Without the common "language" of TCP/IP, there wouldn't be much of an internet.
IP is essentially a unique address for a computer. In a simple internet interaction, the initiating computer has an IP address and so does the receiving computer. TCP breaks the data the initiating computer is sending into packets and then reassembles it at the destination. Along the way, the packets might take separate routes and be routed through numerous other computers, but the IP address ensures the packets get to the right place.
TCP/IP has some vulnerabilities. For example, data packets can get intercepted during transmission over an unsecured connection, such as public Wi-Fi. A solution to this problem is to always use a secure connection like VPN.
