Hypertext : It refers to a digital text that has a unique feature of linking to other documents or web pages.It is generally highlighted in some different colour on a web page.When you click on the hypertext,it opens a new web page.Hypertext may be in the form of text,graphic,video,or audio.It is then called as Hypermedia as it is not confined to only text.
Hyperlink : It is an electronic link providing direct access from a hypertext in an HTML document to another document or an object in the same document.In other words,a hyperlink offers web users reference to data that they can follow by clicking on it.When you hover on a hyperlink,the mouse pointer. changes to the symbol of a hand pointing at the link.
Source code: It contains instructions about the layout and structure of the web page.It also defines the content of the web page.These instructions are used by the browser to dispaly the page.