Programming code that governs how a web service can request information or services .
APIs define three primary elements:
1. Access: Who is allowed to ask for data or services
2. Request: what data or services can be asked for. Requests have two main parts
+ Methods: the type of questions you can ask,assuming you have access.
+ Parameters: additional details you can include in the question or response
3.Response: the data or service for your request.