What is an API? Code runs in the software the part that talks to the outside world, that’s the API. Think of a user interface like logging into reddit a lot of stuff happens under the hood to make the login happen but the public facing part is just two pieces of data: your username and your password, that’s the API. Its two pieces of data that gets sent from the user -> to the front end code -> to the back end. Some code runs in the back end and we send a response back: true if the login worked false if it failed this is called a request and response. Additionally we don’t need a user interface for an API, back end apps can connect directly to each other this is how large companies can scale to thousands of software engineers. Each team has its own app which has its own APIs and the apps communicate to each other with requests and responses. API keys are unique IDs you need to connect to most APIs they’re important for security and preventing APIs from breaking due to sending too many requests which can result in crashing a server.