@sibertAug 18.2019 — #Whenever you want to fetch data from a SQL database (or similiar) you can use REST API.
Basically it is another server listening for a request from your web page to "fetch a list of items" and present them on your website. You cannot fetch data direct from your web page. You must use a REST server in order to communicate with the database server AFAIK.
@NogDogAug 18.2019 — #RESTful API's use a specific URL format and a set of HTTP request headers in order to indicate if the request is a Create, Read, Update, or Delete request (a.k.a. CRUD). Rather than trying to explain it all here, I suspect a simple web search on "restful API" will tell you everything you need, probably better than I would off the top of my head. ;)
PS: While a database is normally involved, that's not required for an API to be RESTful -- just that it follows the relevant URL formats and use of HTTP headers.
@ziptechprivatelimitedAug 20.2019 — #API is the acronym for Application Programming Interface, which is a software intermediary that allows two applications to talk to each other. Each time you use an app like Facebook, send an instant message, or check the weather on your phone, you’re using an API.