TCP/IP stands for Transmission Control Protocol/Internet Protocol. In basic terms, it is the language computers use to find and connect with each other over a network.
In 1969, the Advanced Research Projects Agency of the US Department of Defense embarked on a project to develop a way to share resources securely, which was called Advanced Research Projects Agency Network or ARPANET. TCP/IP was developed during this project as a way for computers to have an easy way to communicate securely.
Over the years, ARPANET grew into a larger community of networks, spanning worldwide in what we know today as the Internet.