Many websites reflect current data or are able to use specialized data from sources such as the National Weather Service, Twitter, Facebook, Governments, etc. This data is not hard coded onto these sites by developers and then changed every-time the data changes. (Could you image trying to hard code a twitter feed that updated regularly a few times a second?) Instead, developers tell the sites the build to access API’s or Application Programming Interfaces. API’s are tools that streamline the process of including data for developers and are provided by those who control the data.
An API allows a developer to write “queries” or requests, that are then sent to a host providers remote server. Assuming the request is valid, and the developer has supplied any appropriate permissions, the server will then send back data pertaining to the request. This data can then be used by the developer’s website to update the contents of the site itself (or whatever application the developer is creating).
Please read the following articles which thoroughly describe what API’s are.