HTML, front end, back end, Sharepoint development, What's the difference between them?

Basm allah alrahman alrahim

HTML hyper text markup language

front end -> in CMS control management system like WordPress it mean website pages , in Computer Definition it is your computer ( client PC ) , in Web development it is the client side interface including apps like evernote or any app at your PC browser

back end the main part of the application at the server , or server side app , at CMS like WordPress it is administration dashboard

SharePoint is a web application platform in the Microsoft Office server suite. Launched in2001,[3] SharePoint combines various functions which are traditionally separate applications: intranet, extranet, content management, document management, personal cloud, enterprise social networking, enterprise search, business intelligence, workflow management, web content management, and an enterprise application store

HTML is a scripting language that a web browser understands. Based on the HTML provided, the browser renders (shows) the content of a web page.

Front end is the PC that you use to connect to web servers (internet ) while Back end are the servers that process the web requests while you surf the web (internet) and provides the HTML to be rendered on the browser of your PC. For your information Browser is an application that is used to surf the internet.

Well I have not used Sharepoint, but it seems to be a platform (like visual studio) to build web pages.

Front end is interface between user and back end and it is collectiong input as various informations The back-end application may interact directly with the front-end or, perhaps more typically, is a program called from an intermediate program that mediates front-end and back-end activities.  SharePoint's information management potential by adding Content Intelligence, which allows you to identify, classify, extract, visualize and surface your information assets better. 

HTML is native markup language for web desiging and development , where front-end is more broad term as Clodelio mention its may refer to everything which render in browser including HTML , CSS , Javascripting etc...

Backend refer to programming languages which compile on server side but these languages final product appear in front-end as HTML , PHP , ASP , Peral , Phthon , Ryby these are few backend languages 

Sharepoint is Application Platform from Microsoft for Wev Development which based on multiple proudcts

Just keep in mind either its any open source backend language or Sharepoint all generate there result in HTML which is native language for Browsers 

HTML and Frontend is synonymous well except that the latter is more broad, e.g. might include CSS, JS, Graphics etc. Backend deals with either database or storage system where anything that is presented on a view layer(frontend) is pulled out from that.