An API response is the data sent back from a server after a request is made by a client, such as a web application or mobile app. This response typically contains information requested by the client, formatted in a way that is easy to understand, often using formats like JSON or XML. The response may include data, status codes, and error messages to inform the client about the outcome of the request. The structure of an API response usually includes a status code, which indicates whether the request was successful or if there was an error. For example, a status code of 200 means the request was successful, while a code like 404 indicates that the requested resource was not found. Understanding API responses is crucial for developers working with APIs to ensure proper handling of data and errors.